The program was called "maths pathway". There are some charts on their website; now that I look at them it looks more like 4-5x. And that was compared to the same school before the introduction of the mastery learning program, I believe.

> Anecdotally, everyone I know who has tried code-learning sites experiences getting stuck (sometimes on a broken problem) and they soon drop out - they don't see the point of progressing any further.

I imagine the situation would be different with an actual human teacher one could ask for help.