He will also say things like "That work is way too easy for me." when he sees the regular first grade stuff. She said she's kind of annoyed by that and has been working on it with him, but she's not judgmental and crabby like your teacher.
I do understand not wanting him to make other children feel less than or being boastful. God knows we have ourselves been on the other end and it so hurts (I do remind DS of that). In fact, I think that is why he really wants to work on and excel in the subjects he does do well and why he is proud of them. And why it means so much to him earn his levels in reading and math. Gotta remember this kid is the only kid in his class who can't write. At ALL. Every day, all day he is reminded, as are all of the other kids, that he can't write . He writes letters and numbers backwards - still. He is the only one. You know how that looks and feels... All the other kiddos write with ease and write well - really well. My kid just can't, and every day he knows it and all the other kids do too... Now his little brother is writing. So maybe she could go a little easier on him - find a way to remind him to be a bit more modest without the public humiliation - sheesh!
