Why are practice tests so effective?

Three reasons stack together: retrieval practice (the act of pulling answers from memory builds memory faster than re-reading), format calibration (you learn what the exam actually looks like), and gap detection (you find what you don't know in minutes instead of hours).

How many practice tests should I take?

At least two full ones, taken under exam conditions, in the week or two before the test. More is better, but two timed papers do most of the work. Use shorter section drills on top for weak areas.

What if no past papers exist for my exam?

Make your own. Write the questions you expect, in the format you expect, from your notes. The act of writing the questions is itself useful: it forces you to think like the examiner.

Should I take practice tests early or late in my prep?

Both. An early diagnostic shows you where to focus. Late practice under timed conditions builds the pace and stamina you'll need on the day.

Is it bad if I score low on practice tests?

No. A low practice score that surfaces gaps you can still fix is worth far more than a high score from a test that didn't challenge you. The point is to find out what you don't know while there's still time.

Practice Tests: Why They're Worth 10x More Than Re-reading

A practice test feels worse than reading the chapter. You sit there, hit a question you can't answer, feel stupid, move on. It's deeply uncomfortable, and it works better than almost anything else you can do with a study hour.

Why they work so well

Three effects stack on top of each other.

Retrieval practice. Pulling an answer out of your head builds memory faster than putting it in. Every question on a practice test is a retrieval rep. An hour of practice testing produces roughly twice the recall of an hour of re-reading on a delayed test.

Format calibration. Exams have a feel: question style, time pressure, expected depth. You can't learn that from a textbook. The first time you experience it should not be on the real exam.

Gap detection. Re-reading hides what you don't know under a layer of familiarity. Practice tests surface every gap in minutes. Two hours of practice tests will produce a more accurate map of your weaknesses than ten hours of re-reading ever will.

The combined effect is why "do practice papers" is the boring advice that consistently outperforms everything cleverer.

How to make practice tests when none exist

For some courses, past papers are easy to find. For others, you're on your own. Make your own. The exercise is itself useful.

Write the questions you'd ask if you were the examiner. Use your syllabus, your lecturer's emphasis in class, and the textbook's chapter summaries.
Match the format. Multiple choice, short answer, essay, calculation, whatever the real exam will use.
Match the length. A 90-minute exam needs a 90-minute practice. Half-length practice doesn't teach you to pace.
Write the question once, take it later. Make the questions at least three days before you sit them. By the time you take the test, you've forgotten enough to retrieve genuinely.

How to actually take a practice test

The conditions matter more than the questions. A timed test in a noisy library tells you almost nothing useful.

Timed, with a clock visible.
Silent, in a room without your usual study comforts.
No looking up answers until the timer runs out.
Full length, in one sitting.

After the test, mark it carefully. Don't just count what's right. For each wrong answer, write a single sentence about why you got it wrong: misread the question, didn't know the concept, knew the concept but couldn't apply it, ran out of time. Each of those is a different problem with a different fix.

The two-test rule

In the last two weeks before any exam, do at least two full timed practice tests under realistic conditions. One four to five days out, one two days out. The first one is for diagnosing weak spots; the second is for refining pace and rebuilding confidence after you've patched the gaps.

If you do this and only this in your final week, you'll outperform classmates who put in twice the hours on flat re-reading. The discomfort is the work.

Questions

Why are practice tests so effective?: Three reasons stack together: retrieval practice (the act of pulling answers from memory builds memory faster than re-reading), format calibration (you learn what the exam actually looks like), and gap detection (you find what you don't know in minutes instead of hours).
How many practice tests should I take?: At least two full ones, taken under exam conditions, in the week or two before the test. More is better, but two timed papers do most of the work. Use shorter section drills on top for weak areas.
What if no past papers exist for my exam?: Make your own. Write the questions you expect, in the format you expect, from your notes. The act of writing the questions is itself useful: it forces you to think like the examiner.
Should I take practice tests early or late in my prep?: Both. An early diagnostic shows you where to focus. Late practice under timed conditions builds the pace and stamina you'll need on the day.
Is it bad if I score low on practice tests?: No. A low practice score that surfaces gaps you can still fix is worth far more than a high score from a test that didn't challenge you. The point is to find out what you don't know while there's still time.