TL;DR:
Blocked practice is ten problems of one type in a row. Interleaved practice mixes the types so that you must decide which method to use.
Mixed sets feel slower and more frustrating, because choosing the method is the extra work they add.
Do a short blocked set to learn a method, then switch to mixed sets to learn when to use it.
You finish a homework section on the area of circles. Ten problems in a row, all answered correctly, and you feel great. The next night, the section is volume of cylinders: ten more, all fine. Then a quiz arrives with a circle, a cone, a triangle and a sphere in random order, and you stall on the first one, not because you cannot do the arithmetic, but because you do not know which formula it wants.
That stall is what interleaving is designed to practise. This article shows the difference with a concrete mixed set and explains why it is worth the extra struggle.
Blocked and interleaved practice, side by side
In blocked practice, you do all the problems of one type before moving to the next: AAAA, BBBB, CCCC. In interleaved practice, the types are shuffled: ABCA CBAB CACB. The total number of problems and the content are the same.
In a blocked set, the method is given away by the section title and by the problem before. You can run the same procedure without thinking about whether it is the right one. Interleaving removes that clue.
Why the mixed set feels worse
Mixed sets feel harder because they are asking for an extra step. Before each problem you have to read it, work out what kind it is, and pick the tool. In a blocked set that choice was made for you.
That extra effort is not wasted. Choosing the method is a real skill, and it is exactly the one an exam uses. Practice that lacks it will feel smooth and still leave you stuck on test day.
What you need
Four to six problem types you have already met once, each with a worked example you understand.
A source of mixed problems. A chapter review or a cumulative test is ideal, or shuffle problems from several sections.
A way to record which method you chose for each problem before you solve it.
Worked example: a mixed set of area and volume problems
Here are six problems from earlier lessons, shuffled. Before solving, write the shape and formula you will use. Then solve.
# | Problem | Method you choose | Answer |
|---|---|---|---|
1 | Cylinder, radius 3 cm, height 10 cm: find the volume | V = πr²h | 90π ≈ 282.7 cm³ |
2 | Circle, radius 5 cm: find the area | A = πr² | 25π ≈ 78.5 cm² |
3 | Cone, radius 3 cm, height 10 cm: find the volume | V = ⅓πr²h | 30π ≈ 94.2 cm³ |
4 | Triangle, base 8 cm, height 5 cm: find the area | A = ½bh | 20 cm² |
5 | Sphere, radius 3 cm: find the volume | V = ⁴⁄₃πr³ | 36π ≈ 113.1 cm³ |
6 | Box 4 cm by 5 cm by 6 cm: find the volume | V = lwh | 120 cm³ |
Recomputing the arithmetic
Problem 1: π × 3² × 10 = π × 9 × 10 = 90π. Since π ≈ 3.1416, 90 × 3.1416 ≈ 282.7.
Problem 3: the cone is one third of the cylinder with the same radius and height, so 90π ÷ 3 = 30π ≈ 94.2. That also checks problem 1.
Problem 5: ⁴⁄₃ × π × 27 = 36π ≈ 113.1.
Problems 2, 4, 6: 25π ≈ 78.5, ½ × 8 × 5 = 20 and 4 × 5 × 6 = 120.
Spot what the mix is doing. Problems 1 and 3 have identical numbers and different formulas. In a blocked set, you would never have been tempted to use the cylinder formula for a cone. Here, you have to look at the shape.
Choose first: Write the method before you compute. If you choose the wrong one, you will find out at the check, and that is the useful mistake. Put it in your error list.
How to set up interleaved practice
Learn each method in a short block first: Do three or four problems of one type until the method is clear. Blocked practice is good for first contact.
Build a mixed set: Pull two problems from each of four or five types and shuffle them so no two in a row match.
Name the method before solving: For each problem, write what it is and which formula or approach applies. Then solve.
Review the choice, not only the answer: After checking, note any wrong choices separately from arithmetic mistakes. They need different fixes.
Mistakes to avoid
Starting mixed before you know any method. Learn first, mix second.
Judging the session by how it feels. A mixed set that feels clumsy is normal.
Mixing too many types at once. Four or five types are enough.
Skipping the label step. Without naming the method first, you may drift back into pattern-matching on the last problem.
Your plan for this week
Take your last three homework sections and pull two problems from each.
Shuffle them and solve them with the label step, timing yourself loosely.
Repeat in three days with a fresh shuffle, adding one more section.
Frequently asked questions
Does this work outside maths?
Yes, wherever the work involves picking among several approaches: chemistry problem types, grammar rules, historical causes. The test is whether the real task asks you to decide which idea applies.
How long before it feels easier?
It may take a couple of sessions. The sense of friction is the part you are practising, so a bit of it is a good sign.
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