The diagnostic test that should open every term

The syllabus assumes a starting point. Your group is somewhere else. Every teacher knows this, and most find out where the group actually is around the fifth week, when a topic that should have taken one session takes three and it becomes clear that the foundation it rests on was never solid.

Test the prerequisites, not the new material

The mistake is testing what you are about to teach. That produces a page of blanks, tells you nothing you did not know, and starts the term with a failure. Test the assumptions instead: the specific things from previous years that this term's content will lean on. If the term needs fluent manipulation of fractions, ask about fractions.

What it should look like

• Fifteen minutes, no more. Any longer and it eats a session you cannot spare and stops happening in future terms.
• Ten to twelve short items, each mapped to one prerequisite. One item per prerequisite is enough at this resolution.
• Explicitly ungraded, and said out loud. A diagnostic students believe counts produces copying, and copied results describe a class that does not exist.
• Marked as a class profile, not as individual scores. What you need is "nineteen of thirty cannot do this", not a ranked list.

Then actually change the plan

This is where most diagnostics die. The test is run, the results are alarming, and the term proceeds exactly as planned because the schedule is already set. If you are not willing to spend a session on a gap the diagnostic finds, do not run it. You will have spent fifteen minutes to acquire anxiety.

A reasonable rule: any prerequisite that more than a third of the group fails gets explicit time before the topic that depends on it, not after.

Keep it and rerun it

The same paper at the end of term is the cleanest evidence of progress you will ever have, and it is far more persuasive to a parent than a grade average, because it shows the same student on the same questions, and nobody has to trust your marking to read it.

Sources

• What Works Clearinghouse — Educator Practice Guides (US Dept. of Education)
• OECD — Education and Skills