Interleaving practice in math leads to significantly better long-term learning outcomes compared to blocked practice.

“the interleaving students who had interleaved practice blew the block practice students away it was I think like the largest effect size I've ever seen an education study there was randomized 0.8 three standard deviations it was like taking a kid in the 50th percentile moving him the 80th percentile but they didn't like it early on they don't feel like they're learning and so I'm not sure what the balance is as a parent where you know some of this desirable difficulty is in the long term desirable but you also don't want to turn someone off from the subject so what's that delicate balance”