10 is a rough age for boys, I have noticed. My son, too, has some trouble concentrating, plus it is getting to be spring & they are getting burnt out with the school year. When it comes to the school work, seek help at his school. Maybe he should miss some recess or get some tutoring so he won't have to repeat this grade.
Also, my son seemed to act out a bit when his little sis was around a year old. I think they miss some of the attention of being "cute" because they are older & the little ones get more of the attention. Try to have him talk to you about things, but I know sometimes they won't. Getting him back into counseling couldn't hurt.
Keep you head up -- I feel for you. Me & my son had a rough year last year with him not wanting to listen or just disagreeing with EVERYTHING I said! But this year, things are much better!