A score tells you something is wrong.
A strong diagnosis tells you where to look next.
Diagnostic resolution is the degree of precision with which assessment evidence can distinguish among competing explanations of performance and identify the next useful repair.
This is the fourth pillar in the second Assessment quartet beneath How Assessment Works. It owns one practical question: how finely can this assessment locate the problem before another piece of evidence is needed?
Quick Read
Not every assessment is designed for diagnosis. A broad examination can rank or certify performance while offering only coarse information about what caused a weakness. Diagnostic resolution rises when the evidence distinguishes knowledge gaps from retrieval problems, method-selection errors, language barriers, execution slips, timing issues and transfer failures. It falls when many different failure mechanisms produce the same score. Strong assessment therefore avoids pretending that one percentage contains more diagnosis than it does. When the result is coarse, ask the smallest follow-up question that separates the remaining possibilities.
Ranking and Diagnosis Are Different Jobs
A test can be excellent at separating higher and lower attainment while being weak at telling each student exactly what to repair next.
That is not necessarily a flaw. It means the instrument has a different job.
The Same Wrong Answer Can Have Different Causes
- concept missing;
- concept present but inaccessible;
- wrong method selected;
- correct method, execution slip;
- language misunderstood;
- time expired;
- transfer failed in unfamiliar representation.
If the assessment cannot separate these routes, the diagnosis must remain broad.
Item Patterns Increase Resolution
One wrong algebra item says little.
A repeated pattern—correct setup, wrong sign manipulation across several items—supports a narrower repair claim.
Response-Process Evidence Can Add Resolution
The first sibling, Response-Process Evidence, can reveal the route behind the answer when the visible score leaves several explanations open.
Aggregation Can Destroy Resolution
The second sibling, Score Aggregation Loss, explains how totals can hide the profile needed for diagnosis.
Conditions Can Mimic Weakness
The third sibling, Assessment Condition Sensitivity, helps distinguish stable capability problems from failures that appear mainly under particular conditions.
Use the Smallest Discriminating Follow-Up
RESULT: poor performance on word problems POSSIBILITIES: - algebra weak - language access weak - modelling weak FOLLOW-UP 1: same algebra without story context IF STRONG → algebra less likely FOLLOW-UP 2: oral restatement of word problem IF STRONG → language less likely NEXT TARGET: modelling relationship
Final Thought: Diagnosis Should Shrink the Problem
The best assessment diagnosis does not produce a larger label. It narrows the uncertainty until the next repair becomes specific enough to act on and specific enough to test again.
ASSESSMENT · SECOND FOUR PILLAR LEGS
Return to How Assessment Works, or continue through Response-Process Evidence, Score Aggregation Loss and Assessment Condition Sensitivity.