I'm beginning to feel like in order to "challenge" my son, I need to drop a Trig book in front of him and walk away.
Actually, maybe you should! That's how my son learned almost all of his math.
I volunteered in a sixth-grade class when I was at uni, and there was a girl there who decided to learn algebra during her in-class reading time - she brought in "Algebra for Dummies". Mind you, she also wrote better than my classmates at university. The thought of what that kid could've done at a school with a proper gifted program makes my head spin. Anyway, BWBShari, there are worse things you could do than drop a trig book in front of your son and tell him to go at it.