cumulative practice

In a nutshell:

if we teach new learning only once all the pre requisite skills are mastered, teaching is more likely to become learning.

timely practice says

This links to mastery learning, if we teach new learning only once all the pre requisite skills are mastered, teaching is more likely to become learning.

It seems that mastery learning doesn't just help learners learn what maths teachers call content skills better (e.g. calculate highest common factor), it also helps learners learn what maths teachers call process skills better (e.g. problem solving). These skills are notoriously hard to teach to lower attaining maths learners.

What educational researchers say

For what we consider higher order skills, such as generalising and problem solving, research suggests, Mayfield & Chase (2002), that when students are using two different pieces of knowledge/skills/methods to learn a third, the students are most successful if both the two existing pieces of knowledge/skills/methods are more strongly embedded before the third is learned. Mayfield & Chase (2002). The effects of cumulative practice on mathematics problem solving. Journal of applied behavioural analysis, 35, 105-123. http://www.gwern.net/Spaced%20repetition