interleaving

Is a type of retrieval practice or spaced learning one of the 4 techniques, associated with learning gain, used by the timely practice system - with the aid of the timely practice app.

In a nutshell:

a type of spaced or distributed learning, where learners practice multiple skills in parallel. 

SRS Learning says

timely practice assignments interleave questions which require a variety of skills, yet the teacher can be sure that each learner can answer most questions independently due to the optimising algorithm of the app. Learners  practise their maths in similar way to an exam tests their maths.

What educational researchers say

"Research shows that interleaving rather than blocking practice of different skills usually improves subsequent test performance."

"This is illustrated by the following procedure from a prototypical interleaving study in which every participant practices four different kinds of skills (a, b, c and d) an equal number of times but in a different order:

Interleaved: abcd badc dcba cdab

Blocked; aaaa bbbb cccc dddd"

Taylor, K. & Rohrer, D. The Effects of Interleaved Practice. Appl. Cogn. Psychol. 24, 837-848, doi:10.1002/acp.1598 (2010). See especially the graph at the top of page 843

The article also points out a fundamental flaw in traditional maths teaching (page 846)

When practice problems are blocked, however, learners can successfully solve a set of practice problems without learning how to pair a problem with the skill. Indeed, because all of the problems relate to the topic—typically the one presented in the immediately preceding lesson—learners can choose the appropriate procedure for each practice problem before they read the problem. While this reduces the difficulty of the practice problems, learners are effectively relying on a crutch.

Meta-analysis (educational research) says:

Perhaps this method is "too young" to have a meta-analysis yet. 

Interleaving is found on the continuum between practise what was just taught to practise anything ever learned. It is found at the end closer to practise what was just taught, whereas timely practice is practise any maths ever learned.

More readable references

Educational Endowment Foundation 

"A Review of Educational Interventions and Approaches Informed by Neuroscience" is informative (page 31) 

https://v1.educationendowmentfoundation.org.uk/uploads/pdf/NSED_LitReview_Final.pdf 

Scientific American

https://www.scientificamerican.com/article/the-interleaving-effect-mixing-it-up-boosts-learning/

Interleaved Practice Jake Jenkins

http://j2jenkins.com/2013/04/29/interleaved-practice-a-secret-enhanced-learning-technique/

A blog from an expert

Robert Bjork The benefits of interleaving