suggestion: end of timed practice
when you use the timed practice on the web site, I find it sad that it will just interrupt you when the time is up.
Two things could be done to improve it (from my viewpoint, that is)
when the timed practice stops, at least show me what the correct solution would have been - so I can at least judge for myself whether I was on the right track or not.
slightly 'better', if time runs out, still wait for me to enter my current answer and show me whether my final answer was correct or not (and what the correct solution would have been) -- only don't add that final answer to the score tally.
In either way, even the final 'task' in the practice would at least help me learn - even if it won't make it into the scoring.