What is the difference between blocked and interleaved practice?

Blocking practices one type at a time (AAAA BBBB CCCC); interleaving mixes types within a session (A B C B C A).

Suppose you're learning to compute the volume of three solids. Blocking means doing all the spheres, then all the cones, then all the cylinders. Interleaving means shuffling them together so you never know which shape comes next. Blocking feels smoother — once you're "in" the sphere block, every problem is a sphere, so you fall into a rhythm. Interleaving feels choppier and harder. That extra difficulty is the point: it is a desirable difficulty, and it changes what your brain is forced to practice.