Hiya stringer - your DS sounds super bright and to be honest I wouldn't be at all worried by a bit of light 'messing about'. He sounds way above average in terms of his ability and progress (compared to my boys any way). For what it is worth my DS1 (Yr2 now) really struggled with the move from R to Yr1 and also turned into a brat at home- a bundle of energy and aggression which was not like him...he is still like that but is still doing well at school. I have accepted that my lovely little boy is growing up and is no longer quite so lovely or quite so little but more demanding and yet real fun! My DS2 is now in Yr1 and found the transition easier but I am awaiting his hormone rush with some trepidation! Not quite sure who has instigated reward charts as his behaviour sounds far from disruptive. My only slight concern would be if he was bored and not being stretched enough...
My DS, also April born Y1, has difficulties concentrating when listening to the teacher or in assemblies. We had sharing assemblies with parents there and I watched him: came in and sat there all straight and smiling, 1 minute in he started yawning, picking his nose, almost falling asleep and had to be reminded and pushed when it was his turn - I thought he was tired but afterwards he was his chatty self again.
I saw him in class as well, listening to a story and questions etc. quite a long time sitting and listening on the carpet (35 min.) - which I thought was too long. DS did not listen, I could see that and he then couldn't do the group task either, neither could any of the boys on his table though (mixed Y1/2 class) - I did find that a bit worrying.
His teacher told me that DS is doing very well but could improve on his concentration and that he was not the only one. She gave me a sheet with some ideas on how to do that, but apart from reading my DS does not do puzzles, play games by rules - so that didn't help.