My 2nd grader's school marks haven't been so great, can someone share or help in their experience?

Hi everyone, and thank you for reading my question. To make a long story short, I picked my son up from an afterschool program and found him misbehaving. It was very bad and embarring. He was laid atop the table with another clmate of his during the program. They were supposed to take a cl picture and they did not want to cooperate. The sub-teacher looked seemed frustrated and so were the students. I have never seen him exhibit this type of behavior before, but it is not often I am at the school to watch him day by day. It shows in his grades. He got a few S's in work habits (following the rules, doing what he is told, being courteous, exhibiting self-control). I have been letting him go outside more and it seems thats what he is more focused on when he gets home from school. Because of being so upset, he had no privledges and from this point forward I am going to be really tough with him. He was very remorseful after a long talk (plus one before bed and another before he left this morning). I told him that it is not in any way acceptable to act like that in school or anywhere else. No matter who it is you must listen and follow the rules. He told me it was because it was a sub (I remember how that was), but I was furious seeing it for myself. Hopefully, things will change and he will improve in the cl. I'm thinking about having a conference with his teacher. Otherwise, his academic marks are still good (O's and G's, and an S in written comm.) He's always done well in school, but I think this year he's showing some lack in self-control, following rules. I'm sure there are things I can work better at home to improve his behavior in cl. Anyone with suggestions, comments, experience, help is greatly appreciated. Thank you for your time.