CK-12 for Students | Free Maths and Science FlexBooks

CK-12 for students brings together free digital textbooks, interactive Science models, Mathematics explanations and practice questions. A learner can read an idea, inspect a diagram, work through a calculation and try questions in the same general learning environment. That combination can be useful for filling gaps that schoolwork has revealed.

But a free online textbook is not necessarily a complete match for the Singapore syllabus, and an automatically marked practice question cannot always identify why a pupil is confused. A child may know the definition of an equation but still manipulate it incorrectly, or watch a Science simulation without understanding its assumptions.

Parents searching for CK-12 free textbooks, CK-12 FlexBook, CK-12 adaptive practice, CK-12 Science simulations, or CK-12 for Singapore students need a practical guide to choosing relevant material, interpreting feedback and checking what the learner can do without the screen.

Quick answer: CK-12 provides free online educational resources, including FlexBook 2.0 textbooks, adaptive practice, interactive PLIX activities and simulations. Its official FlexBook guide describes these learning resources. The best routine is identify one weak concept → study the relevant explanation → explore one representation → practise independently → check the first error → revisit a different example.

What Is CK-12?

CK-12 is an education platform developed by the CK-12 Foundation, with a focus on freely accessible learning content and tools. Its resources include structured digital textbooks and related Mathematics and Science materials.

The term FlexBook refers to its adaptable textbook content. Unlike a static scan of a printed book, many FlexBooks are designed for digital study, with explanations, illustrations and linked exercises.

An individual learner may read a chapter about fractions, algebra, motion or Chemistry. A teacher can select relevant concepts and assign materials to a class under supported workflows.

The important advantage is proximity: the explanation, interactive example and practice can be available from one place. A pupil does not have to search for a separate answer key every time they reach a new topic.

The limitation is that content is still organised within the publisher’s own educational framework. Teachers and parents must select material that actually matches the child’s current learning gap.

Is CK-12 Free?

CK-12’s official explanation of its resources describes its digital textbooks, adaptive practice, interactive learning tools and related school materials as freely accessible.

This is one of its distinguishing features. A parent need not begin by purchasing a large Mathematics course before checking whether a CK-12 explanation helps with a particular concept.

However, free availability should not be mistaken for a claim that the content will automatically replace every national curriculum or examination specification.

A resource may be excellent for explaining linear relationships but cover a different topic order or set of required methods from the student’s Singapore school.

Choose the correct topic first. The price and interface are secondary to whether the explanation helps the learner understand and apply the concept.

Some features require an account or school-managed assignment workflow to record individual progress; access arrangements should be checked within the current service.

What Is a FlexBook 2.0?

CK-12’s FlexBook 2.0 overview describes a textbook environment integrating core lessons with interactive experiences and practice.

An individual lesson can include text, images, examples, PLIX interactives, simulations and practice material. The official lesson-features guide also describes controls for highlighting, display settings and accessing relevant resources.

For a child studying algebraic expressions, this means the learner can read the explanation and then attempt questions associated with the same concept.

But the lesson should not be treated as complete after only scrolling to the bottom. Reading and recognition are weaker evidence than independently solving a changed problem.

A parent can ask: What is the main principle you learnt? Which step did you find difficult? Can you show another example without looking?

That conversation turns digital textbook use into visible learning.

Conventional and Interactive FlexBooks

CK-12’s textbook comparison guide distinguishes conventional and more interactive FlexBook formats.

A conventional textbook can suit a student who needs sustained explanation and a familiar reading sequence. An interactive format can provide exploration through activities and linked representations.

The best choice is not simply the more animated one. Some pupils need to read an accurate explanation slowly. Others benefit from manipulating a model or receiving feedback on small practice questions.

A student learning a new Science term may begin with a short paragraph and diagram. Once the idea is understood, an interactive activity can test a relationship or help with transfer.

Choose the format according to the first weakness: comprehension, visualisation, method selection or retrieval.

The educational question remains the same whichever book type is used.

What Are PLIX Interactives?

PLIX stands for Play, Learn, Interact, eXplore. CK-12 uses PLIX activities to let learners experiment with selected Mathematics and Science relationships.

A simple interactive might allow a student to change values, compare representations or see the effect of an input on a mathematical or scientific model.

This can help reveal a concept that is difficult to understand from words alone. A pupil might be able to describe a proportional relationship more confidently after seeing how two quantities change together.

But the learner should predict what will happen before moving a slider or changing a value. Otherwise the result may be interesting without being conceptually understood.

After the interaction, ask for an explanation in ordinary language and a separate worked example on paper.

An interactive is educational when it turns an observation into a transferable principle, not merely when the child completes its animation.

Worked Example 1: Equivalent Fractions

Suppose a Primary learner is unsure whether 3/4 and 6/8 are equivalent.

Three quarters means three of four equal parts of a whole. If every quarter is divided into two equal pieces, the same shaded amount becomes six eighths.

Mathematically, multiplying the numerator and denominator of 3/4 by 2 gives 6/8. The represented amount has not changed.

The student can use a visual example or interactive fractions model to inspect that equivalence, but should also explain the numerical relationship.

Now compare 3/4 with 3/8. The numerators are equal, but the parts have different sizes for equally sized wholes. Three eighths is smaller than three quarters.

A useful independent question is 2/3 = 4/6. Ask the pupil to draw or explain why the fractions are equal without a digital prompt.

The concept is not simply recognising which picture is darker. It is understanding how numerator, denominator and equal parts determine a quantity.

Worked Example 2: Adding Fractions Without a Shortcut Error

Consider 1/2 + 1/3. Some learners add numerator to numerator and denominator to denominator, obtaining 2/5.

That is not a valid general method for adding fractions. The two fractions describe different-sized parts, so they must first be represented using equal units.

One half equals three sixths, and one third equals two sixths. The sum is 3/6 + 2/6 = 5/6.

A visual representation can show the same whole divided into sixths with five parts shaded, but the child should connect the picture with the arithmetic.

Now offer 1/4 + 1/2. Rewriting one half as two quarters gives 1/4 + 2/4 = 3/4.

If the learner can perform and explain the new example without the earlier image, the understanding is becoming independent.

More repeated digital clicks will not repair the original misconception unless the student understands why a common denominator is needed.

Worked Example 3: Algebra and the Distributive Property

A Secondary 1 student is given 3(x + 4) and writes 3x + 4.

The error is failure to multiply the second term in the bracket. The correct expression is 3x + 12.

Explain that three groups of x + 4 contain three x terms and three groups of four. The distributive property is a statement about how multiplication operates over addition.

A numerical check uses x = 2. The original expression is 3(6) = 18. The correct expansion gives 6 + 12 = 18; the incorrect expression gives 6 + 4 = 10.

Then solve the related equation 3(x + 4) = 21. Divide by three to obtain x + 4 = 7, so x = 3. Verify the solution in the original equation.

The final independent example might be 4(x + 5) = 32. The learner should obtain x = 3 while explaining the method.

CK-12 can provide practice, but the student must still justify each algebraic step.

Worked Example 4: Why Dividing by a Variable Can Lose a Solution

Consider the equation x² = x.

A pupil may divide both sides by x and conclude that x = 1. The problem is that this division assumes x is non-zero.

Instead, rearrange: x² − x = 0. Factorise: x(x − 1) = 0. Therefore x = 0 or x = 1.

Both satisfy the original equation. If the student divides by x without checking the zero case, a legitimate solution is lost.

A textbook explanation should help the learner understand the condition behind an operation, not merely memorise a faster manipulation.

Ask why dividing by zero is undefined, and whether cancelling a factor is always safe when the factor may equal zero.

The lesson illustrates that mathematical reasoning requires tracking conditions throughout a calculation.

When checking an answer with software, substitute all proposed roots into the original problem.

Science Simulations: Helpful Models With Limits

CK-12 also provides interactive simulations linked to scientific concepts. Its help explains that these can be embedded alongside reading and practice.

A simulation might demonstrate motion, force, electricity or energy in a simplified environment. The pupil can explore what changes when a relevant condition is modified.

However, a simulation is a computer model, not direct physical evidence about every real-world situation. It behaves according to programmed rules and chosen assumptions.

Ask students to distinguish what the model displays, which principle it is intended to represent, and what real conditions might differ.

For instance, a virtual circuit may assume ideal components that behave more predictably than a real damaged wire or discharged battery.

Simulations are strongest when they motivate precise questions and independent explanations. See PhET Simulations for Students for a related learning method.

Worked Science Example: A Simple Circuit

Imagine a diagram with a battery, a bulb, wires and a switch in a simple series path.

When the switch is closed and the components are appropriately connected, a complete conducting circuit allows current through the bulb. When the switch opens, the intended path is interrupted and the bulb goes out.

An incomplete explanation such as the battery has disappeared is physically wrong. The battery remains part of the circuit; the relevant change is the conducting connection.

A CK-12 lesson or simulation can help illustrate this relationship, but the learner should describe the underlying process without the animation.

Ask a fresh question: What happens if a connecting wire is disconnected instead of opening the switch? In the same simple series path, the loop is broken and the bulb cannot remain lit under the stated conditions.

The educational goal is understanding the cause rather than recognising a particular switch icon.

For the broader Singapore Primary approach, see How Primary Science Works.

Worked Science Example: Energy Transfers

A student might explore a model of an object descending a slope.

As the object moves down, its gravitational potential energy can decrease while kinetic energy increases, depending on the physical conditions.

In an idealised frictionless model, mechanical energy may be conserved. In a more realistic model, friction transfers some mechanical energy into thermal energy.

The learner should not conclude that energy vanishes merely because a moving object slows down.

Ask what the model assumes. Does it include friction, air resistance or other losses? Is it treating the object as a particle, or modelling rotation as well?

Then request a written explanation of a different case, such as a pendulum swinging between its higher points and lowest point.

A correct explanation identifies the relationship and the assumptions; it does not simply repeat the label on a simulation graph.

What Is CK-12 Adaptive Practice?

CK-12 provides Adaptive Practice associated with certain lessons and concepts.

Adaptive practice aims to respond to a learner’s performance and give useful information about skill development. A teacher may see practice metrics or targeted recommendations when the appropriate reporting features are available.

This is helpful for locating possible problems, but the result cannot automatically reveal the cause of every mistake.

A wrong fraction answer may reflect an unstable concept. A wrong typed response might involve a notation error. A pupil may also misread a word problem because of English comprehension.

Use the results as diagnostic clues. Then inspect the first wrong reasoning step and ask the learner to explain what they intended.

A progress display should guide the next teaching decision, not serve as an official examination prediction.

Flexi: An AI Tutor Is Not an Official Answer Authority

CK-12 has developed Flexi, an AI-supported tutor that can help with questions, hints and practice, as described in its accessibility and platform overview.

A student may find it useful to ask for a simpler explanation or help diagnosing why a mathematical step does not work.

However, AI-produced text can misinterpret a question, provide a method unsuitable for the pupil’s level or generate an incorrect claim.

Check important calculations by substitution, compare Science statements with appropriate source material and follow school requirements for assessed work.

A safe and educational prompt might ask Show me one simpler example without giving my homework answer.

If the student cannot solve a changed problem after reading the hint, more teaching is needed.

A capable learner should gradually require less help for the same concept.

Classes, Assignments and Teacher Feedback

CK-12 supports class creation and teacher-assigned materials. Its educator guide explains access to content, classes and assessments.

The current class guide describes inviting pupils, assigning suitable resources and monitoring progress under authorised classroom accounts.

Teachers should choose an assignment based on one clear learning objective, even if they plan several concepts across a week.

CK-12’s July 2024 assignment guidance explains the shift toward a single-concept-per-assignment approach for better diagnostics while retaining the ability to assign several lessons with separate dates.

This is useful because a general low score in a long mixed assignment may not reveal whether the issue is fractions, negative numbers, graphs or English question interpretation.

Clear teacher instructions and individual feedback remain essential.

CK-12 and Google Classroom: Two Completion Steps

A particularly important workflow issue is documented by CK-12 itself.

Its Google Classroom add-on instructions explain that a learner may need to complete the CK-12 activity and choose Mark Complete in the appropriate CK-12 lesson or practice, then select Turn In inside Google Classroom.

For some activities, CK-12 may record completion automatically, but the Classroom assignment can still require the separate Turn In action.

This distinction is familiar to families who have encountered a saved document that was never submitted.

The child must check both the academic answer and the official assignment state. Completing a digital practice exercise is not necessarily proof that the teacher’s workflow has recorded the task as turned in.

See Google Classroom for Students and Parents for the broader submission process.

Is CK-12 Aligned With Singapore MOE?

Some mathematical and scientific ideas are universal, but curriculum structures differ. An international grade label does not automatically correspond to Singapore Primary 5 or Secondary G2 Mathematics.

A CK-12 explanation of equivalent fractions may fit the child’s immediate foundation gap. A Science chapter may use a model, depth or sequence different from the teacher’s current expectations.

Singapore learners should check the current school textbook, assignment and relevant MOE syllabus before choosing practice material.

For Secondary Mathematics, select the skill based on the child’s actual subject level, such as equations, graph interpretation or a specific Geometry concept.

For Science, check that scientific terminology and the level of explanation match the student’s assessment.

Do not claim that finishing a CK-12 course means the complete PSLE or SEC curriculum has been mastered.

Use the platform to strengthen understanding within a school-aligned learning plan.

CK-12 for Lower Primary Learners

Young children may need adult help choosing a suitable topic and interpreting instructions. A full digital textbook chapter may be more demanding than a short practical example.

Start with a concrete number or shape relationship. A simple counting or fraction representation can be explored with physical counters before introducing digital practice.

If an interactive activity uses unfamiliar language, explain the task rather than letting the child click randomly.

Ask the pupil to reproduce the idea on paper, using objects or a drawing.

The aim is to build conceptual meaning. The technology should not make a simple task unnecessarily complicated.

Where the child’s curriculum requires early reading support, choose appropriate English instruction alongside the Maths activity.

CK-12 for Secondary G1, G2 and G3

At Secondary level, the breadth of CK-12’s Mathematics and Science materials can help a learner revisit foundations or explore selected concepts more deeply.

A student who struggles with the distributive property can focus on algebraic expressions. Another who reads a graph incorrectly may need to connect equations, axes and tables of values.

Higher-level material should not be introduced solely because the website recommends a more advanced topic. Check the child’s school sequence and current readiness.

For G3 and Additional Mathematics, a graphical explanation may assist intuition, but students still need the exact symbolic methods and written reasoning expected in assessment.

A good tutor can use CK-12 as one support among textbook work, discussion, varied questions and timed practice where appropriate.

Progress is better measured by independent performance than by the quantity of digital material completed.

CK-12 Versus Khan Academy and PhET

Khan Academy for Students combines sequenced video explanations and exercises in supported courses.

PhET Simulations for Students specialises in interactive educational models. CK-12 combines textbooks, assessments and several interactive tools within its own framework.

No single option is always best. A child who needs a careful written explanation may prefer a FlexBook lesson. A student exploring a physical relationship may benefit from a simulation. A learner needing targeted procedural practice may benefit from a short assessed exercise.

Do not make a pupil repeat the same weak explanation on three platforms. Identify the first unstable concept and choose the method most likely to repair it.

The software should make the teacher’s diagnosis more precise, not replace that diagnosis.

A Twenty-Minute CK-12 Study Routine

Use one specific concept rather than opening several unrelated chapters:

Minutes 1–4: Identify the current weak skill from actual schoolwork.
Minutes 5–8: Read or listen to the relevant FlexBook explanation and note one key principle.
Minutes 9–12: Try a PLIX, simulation or short example when it genuinely clarifies the concept.
Minutes 13–16: Complete a few practice questions without guessing.
Minutes 17–18: Examine the first wrong answer and explain its cause.
Minutes 19–20: Close the tool and solve a fresh related problem independently.

For a three-student tutorial, rotate reader, reason checker and solver. Each child should make an initial attempt before seeing the group’s answer.

If the independent attempt fails, identify whether the student needs a simpler model, a more precise verbal explanation or additional practice.

The purpose is the next reliable answer, not a longer session online.

Accessibility, Devices and Learning Conditions

CK-12’s accessibility statement describes browser access across device types and support for multiple learning formats.

It also notes that standalone simulations and PLIX interactives generally work better on a tablet or larger display due to their interface size.

This matters for a student attempting a complex diagram on a small phone. The failure may arise from cramped controls rather than lack of Science understanding.

The FlexBook experience may include changes to text size, line spacing and display settings. These can support learners who benefit from more comfortable reading.

Use printed or offline material where suitable and permitted. A pencil drawing is sometimes clearer than manipulating a complicated interactive on a small screen.

Accessibility should make the intended concept easier to learn, not introduce unnecessary obstacles.

Privacy, School Accounts and Original Content

Students should use authorised school accounts and the class joining method set by the teacher. Account permissions and progress reporting depend on the classroom configuration.

Do not upload confidential school tests, private pupil records or personally identifiable information into public resources.

CK-12 provides freely accessible learning content, but copyright and licensing conditions should still be checked before redistributing a modified textbook outside the intended setting.

Teachers can adapt materials within the service’s permitted framework; students should distinguish their own explanations from sourced material.

A private notebook recording one student’s misconception generally requires less personal information than an entire shared class report.

A good digital learning system protects both accurate understanding and student privacy.

Frequently Asked Questions

Is CK-12 free?

CK-12 describes its digital textbooks, adaptive practice and learning tools as free resources. Account and class workflows may have different setup requirements.

What is a FlexBook?

A FlexBook is CK-12’s free, adaptable digital textbook, sometimes including interactive lessons, simulations and practice in the same environment.

What does PLIX mean?

PLIX is CK-12’s name for interactive exploration experiences, short for Play, Learn, Interact, eXplore.

Can CK-12 help with Singapore PSLE Maths?

It may strengthen relevant concepts such as fractions, measurement and operations. It is not a complete replacement for Singapore syllabus-based word-problem and assessment preparation.

Does CK-12 use adaptive practice?

Yes, for supported concepts. Such practice can help reveal gaps, but it does not substitute for independent explanation or an official school grade.

What is Flexi?

Flexi is CK-12’s AI-supported learning assistant for suitable questions, feedback and hints. Students should verify calculations and important factual claims.

How do assignments work in Google Classroom?

Some CK-12 assignments require marking the activity complete within CK-12 and then selecting Turn In in Google Classroom. Follow the exact school workflow.

Can I print CK-12 materials?

CK-12 help documents printing or downloading certain practices and quizzes. Availability and formatting depend on the specific resource and relevant permissions.

How can parents check whether CK-12 helped?

Ask the student to explain the concept and solve a changed question with the online textbook closed, ideally again after a short delay.

Official Sources and eduKateSG Learning Routes

The lasting lesson: CK-12 can make high-quality explanations and practice easier to reach. Understanding becomes real when the child can select the right principle, justify it and solve a new problem without the textbook.

CK-12 for Students | Free FlexBook Textbooks, Maths and Science Practice