[ndriscoll]

The neat thing about stratifying by ability is that it doesn't require any additional resources or special programs. If you have 20 teachers in a school, you divide the student population into roughly 5%-wide ability bands instead of roughly 5%-wide age cohorts with random ability, and that's it.

Mastery learning is also more effective than moving on with knowledge gaps, so this should be expected to raise everyone's outcomes.

[WillAdams]

Exactly. The school was laid out in grids, and identical layouts between floors (higher grades higher up) with identical class sequencing for each grade, so at class change time, it was easy for even young kids to get to their next class.