ProfEd Assessment of Learning — LET Practice Questions

Diagnostic assessment happens before teaching to identify what students already know and what gaps or misconceptions they hold. A pre-test at the start of the school year reveals that some students are strong in fractions but weak in percentages, or that some understand place value while others do not. This information guides lesson planning, grouping, and pace. Diagnostic assessment answers the question What does this student know right now? It is the starting point for responsive teaching and helps prevent teaching material students already mastered or missing prerequisites they need.

A difficulty index of 0.15 means only 15 percent of students answered the item correctly. By the convention used in classroom test analysis, that puts the item in the 'very difficult' range. The index alone doesn't say WHY it's difficult — the item could be genuinely hard, poorly worded, ambiguous, or testing content the class hasn't covered. Teachers usually pair the difficulty index with the discrimination index (how well the item separates high-scorers from low-scorers) to decide whether to keep, revise, or discard it. A difficulty of 0.15 paired with low discrimination usually means the item should be revised or replaced.

A test item has two jobs: be at the right difficulty level and separate high performers from low performers. A difficulty index of 0.92 means 92% of students got it right, so almost everyone passes it, making it too easy. But worse, the discrimination index of 0.05 means the item does not separate strong students from weak ones; even weak students are getting it right by luck or because it is trivial. Together, these numbers signal the item is not useful for assessment. For example, if an item is 'What is 2+2?' many will answer correctly, but so will students who just guess. Such items should be discarded to save time on the test and focus on items that reveal true understanding.