Why blocked practice can mislead
Blocked practice — twenty problems of the same type in a row — feels smooth because by problem three you've stopped deciding which method applies and are just reapplying it. Mixed practice forces the real exam skill: looking at a fresh problem and working out what kind of problem it even is.
Use it where topics are confusable
Interleaving shines when topics are confusable: integration techniques, muscle groups, philosophers, chemical reaction types. It helps less for isolated one-off facts.
Expect the session to feel harder
Expect it to feel worse. Mixed sessions produce more errors while you practice and better scores when it counts — that trade is the point.