I'm interested in things that you feel advance their understanding of math, sciences etc.
My oldest son is 10 and in Grade 5, and I feel like the classroom curriculum is targeted at the slowest student, and the average and above-average students aren't challenged enough.
For example, he is learning about spelling and reading right now. I asked him what things he would like to watch on youtube, (robots) and then we spent time learning how to spell that word together so he could find a cool video on robots.
For art (which he doesn't like very much) I've been getting him to draw out designs for things he wants and then I build them out of wood for him. So while he is not painting beautiful rainbows or anything (yet) he has designed some cool amphibious vehicles and Mars rovers which I went on to make for him.
It seems to be working so far - but hey, I am only a month in. The key seems to be in getting him to figure out what he wants to use the information for.