Off-task, inattentive, not focused are all code words schools use for ADHD. They are hoping that by using these words, you get it. Your DS actually sounds exactly like my DD when she was 6. I kept asking "Do you think she has ADHD?" and no one would give me a direct answer. Schools don't want to suggest "ADHD" because they are not allowed to diagnose kids and don't want you to sue them.
Is he focused at home? For instance if you asked him to write a couple paragraphs about anything that he wants, would he get down to work and do it quickly? Or would he need reminders to stay on task? If you give him written math at his level does he stay on task? Is he disorganized, messy, need reminders about everything? If he also has problems focusing at home, then I would seriously consider ADHD--otherwise you are probably onto something with him being completely bored and disengaged at school. But remember kids with ADHD CAN focus on things if they are engaged (for instance my DD can do complicated puzzles and read long books even when she's not on medication)--you have to give him something that is is not fascinating to him to see if he can focus.
