Retrieval practice and spaced learning

How many questions should I give students to work on after my instruction? Should I group all the questions together or space them over time? Should I ‘block’ questions on the same topic together or should I mix them with questions from other topic areas? Is ‘over-learning’ an efficient strategy for boosting student outcomes? Should I always be using high-frequency formative assessment techniques to guide my instruction? Is it possible, and if so, how do you measure the learning that has happened in a lesson? What does best practice look like in an assessing-without-levels world? Within a progress context, are rapid and sustained mutually inclusive or exclusive?

http://www.greatmathsteachingideas.com/2015/01/20/forgetting-is-necessary-for-learning-desirable-difficulties-and-the-need-to-dissociate-learning-and-performance/