I just put it on hold at the library. My 5yo seems advanced, but I haven't had her tested. Is the book helpful for someone whose child hasn't been tested, and won't be anytime soon?

Do you think you can honestly get an idea about level of giftedness without formal testing? The reason I ask is because DD is moving through material quickly, and has much broader comprehension than I expected. I'm trying to understand her better, since I'm her teacher (we homeschool).