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.
We had this problem. My son didn't pay attention when filling out the counting sheets, and then later the "1+1" sheets, and would get the answers wrong because he was rushing through it to be finished. (He apparently made it a game to see how quickly he could finish.) The teacher really thought he hadn't mastered counting or basic addition, although at home he was working on square roots and multiplication. He used to write more difficult problems in the margins - somehow that never made an impression on her, though. Having to complete homework at that level all year really caused problems for my son by the end of the school year. Talk to the teacher asap and see if you can substitute harder worksheets or if she will give him something else. At our school, it couldn't just be ignored - students would be kept in from recess to finish homework that wasn't completed, even in K.
