I've been doing "school" with Alex and Holly for a few months now. It's one of their very favorite things, but then, we're not doing anything real major.
I print materials off this First School website, whom I found through AAA Math. We've been working our way through the alphabet by making little books for each letter.
Each little book has stickers that you cut out and put in. I just use a little roll of tape on the backs.
And a little handwriting bit where they can trace the letters. Alex really enjoys these.
Maybe I should print him the actual handwriting pages.
Then we do a coloring page with one of the things starting with that letter. In this case, it was a mouse, since we were doing M.
School is their favorite time of day, and we usually do it as soon as I've had a shower, so, like, 7:30 AM. It's a bit early for me, but it sure makes their day.
We do math a little less frequently. We count things, and say the numbers as the microwave counts down. I figure that's about as in-depth as we need to get.