Clothespin Math on a clothes hanger! LOVE this. Easy to make, and self explanatory. I'm thinking a wire clothes hanger would work better, so the clothes pins are easy to slide back and forth (almost like an abacus).
This activity can help children with angles. Instead of measuring angles on paper, this can illustrate angles into a read life demonstration. This is active learning because as children close the door the angle changes and they can now measure it.