I'm just worried that if I push for something more, the teacher will come back saying DS5 makes mistakes, meaning he hasn't master the topic. I haven't seen any mistakes on his work ... YET ... but knowing him he will start making them because when he does stuff that's too easy, he doesn't pay any attention to it and will just mark "whatever" to be done with it.

I am honestly regretting even sending him to K (though it's just a half day). The only real reason we sent him in was that I desperately need some QUIET (he talks nonstop all the time, no matter what he's doing) AND I need the couple hours alone time for one on one work with DS3 (to work on his anxiety and speech delay).