Jai,
I would wonder if there's something more to the frustration and anger than simply frustration and anger. You mentioned in your letter to the school that your ds had scored relatively low on one component of Dibels, and the school didn't follow up with you on that. You also mentioned that your ds has said that this year the work is hard, he doesn't always know the answers, and it takes him a long time to write his name. It's possible those comments are simply coming from a child who was previously in a classroom that required no work and now he's in a classroom with higher-performing peers and higher work expectations... but... the same comments (combined with his Dibels score) *might* indicate he has some type of learning challenge. Kids who have learning challenges don't typically know how to articulate them well when they are in early elementary, and their frustration can sometimes present as behavior challenges in the classroom.
It's also tricky for adults to recognize challenges in early elementary, because the "normal" range of development for reading/writing etc varies so much among different children.
I'd not punish him at home for behaviors that were an issue at school. I'd talk to him about it, explain what's expected and what he should be doing, and also listen to his explanation of what happened. I'd also be sure I fed him at least a small snack right away after school. Only mention that because my gang always comes home from school hungry - and trying to piece together what's going on with a report from school etc will probably be easier if your ds isn't on a blood sugar low. Might not be a problem for him - but it's huge for my kids
To be honest, I might even think through when the behaviors are occurring during the school day - is there any correlation to when kids eat (i.e., issues occur before lunch or late in the afternoon).
Best wishes,
polarbear
