I think children often change their outward behavior at this age. Of course, that doesn't mean he is not still the same caring boy underneath that he always was. When I recently attended my ten-year-old son's school parent's consultation, I was surprised that the feedback was entirely different from every other consultation I had attended for him. My son had been messing about much more in class with his friends, although he is still meeting his targets and doing well from an academic view. Previously to that, he had always had a lot of friends but been very conscious of behaving properly during lessons.
The teacher, however, said that children of this age are becoming much more conscious of how they appear in front of their peers.
In my limited experience, children are often not very enthusiastic about homework! Seeing the value in education is something that he will probably come to view when he is older; however, to an eleven-year-old, the future probably seems very far away! I can tell you that my eldest son, who is now about to turn eighteen, become much more severe about from the age of 15/16 if that is any consolation! Before that, he was frustratingly laid back about it all!
Perhaps you could encourage him by offering him small rewards if he makes a good effort with his homework? I agree it can be a very trying time - good luck!