Its week one, and though the behaviour is unacceptable, my opinion/advice would be very different if this had gone on for a long time.
He's still settling. Obviously you need to address it, rather than just say 'well its your first week, carry on' but I wouldn't WORRY too much about it. Stick with what you'd usually do in naughty situations.
The whole first year of school is a massive social adjustment to children but most do settle!
My sons' teachers are interested in what's going on at home. It helps them, their information helps me (my son is a DIAMOND at school, a bit of a bugger at home) - many of the school's tactics can help at home as well.
Purely for consistency, we put my eldest on a 'traffic light' system (not actually tied to actual traffic lights, though it was tempting) as that was the stepping stones to 'punishment' that school used... it worked a treat. He never got past amber. Basically its a traffic light, and a sticker (we used a fridge magnet) good behaviour and they're in the green, a bit wobbly they're in amber (and on a final chance/last warning) and red means no priviledges... what they are is up to you, but on RED, my eldest got no TV, no Friday sweets, no Wii, until he was back in amber, and then it was very limited.... in GREEN, he didn't get spoilt, but its the expected state, so usual rights, treats and priviledges applied.
For truly superb behaviour, a month of Green for example, we'd go bowling, or to the cinema, or he could whatever he liked... we only used this system for half a term, as it was needed. We haven't done it since, but would reintroduce it in a flash.
Sorry for long post!!