Wow, that's an awesome picture. He really captured a lot of energy and expressiveness there. I can see you as a superwoman, a whirlwind of Mom-competence, dealing with everything at once!
If his teacher thinks that stick figures show little effort, it's clear that she isn't familiar with
XKCD , one of the most popular comics on the Web.
What's her problem with abstract art? If he regularly drew more representational pieces, and just wanted to use stick figures on this assignment because he didn't want to bother making an effort, I could see her point, but that's not the case here: this really is his preferred form of artistic expression. I wonder if she realizes how painful it is for a child, or for anyone, for that matter, to be told that their vision, personal expression, and way of being is wrong and worthless? I think this goes way beyond a question of grades.
