A worksheet is a sample, not a stack

You are about to hand out twenty problems. There are millions you could have picked. The twenty on the page are a sample — of a topic, of a difficulty, and of an order — and every one of those three is a decision whether or not you make it consciously.

Start with the one that changes results the most and gets the least thought: the order.

The same twelve problems, twice

Blocked practice groups a topic together — four multiplications, then four divisions, then four percents. It's what a chapter worksheet looks like, and it feels productive: after problem two, the student stops reading the instruction and starts running the procedure. Speed climbs. Errors fall. Everyone feels good.

Interleaved practice mixes them so no two neighbors share a topic. It's slower, it feels worse, and the student has to answer a question the blocked sheet never asked: which method does this one need?

That question is the whole point. In the exam — and in every situation after school — nobody tells you which chapter the problem came from. Blocked practice trains the steps. Interleaved practice trains the choice of steps, and the choice is the part that transfers.

The honest version of the claim: interleaving reliably produces worse performance during practice and better performance on delayed tests across a large body of cognitive-psychology studies. It's one of the more robust findings in the field — and still a finding about averages, not a law about your Tuesday class.

What this means for the sheet in your hand

Both are legitimate; they do different jobs:

The generator does both without a setting called "interleaving": pick a single topic and you get blocked practice; pick Mixed review and you get a sheet drawn from a pool of topics, which is interleaved by construction.

The other two samples

Difficulty is a sample too — a 2-digit multiplication sheet draws from a different space than a 3-digit one, and the difference is stated, not felt. That's the next lesson.

Count is the one people over-think. Twenty problems of a method the student already owns is twenty minutes of copying. Six problems chosen so that no two use the same approach can be a harder, better assignment. When you halve a sheet, you're not being lenient — you're deciding that the remaining problems have to carry more weight each.

Run it

Open the worksheet generator with a single-topic sheet loaded:

1. That's blocked practice: ten problems, one method. Scan it and notice you could solve it without reading each instruction.
2. Switch the topic to Mixed review 2 — everything at the same difficulty. Same count, same level, and a completely different task: every line now starts with a decision.
3. Print both. Hand one to a class in week two of a unit and the other in week five, and you've used the same tool for two different jobs.