DD was similar, although oldest in the class. Losing interest in school, switching off when previously engaged. She told us the class was noisy and she couldn't concentrate.
DD had to sit next to TA to produce any work, as lost focus and distracted, but in small groups or on her own worked well. However this wasn't the child we could see at home, she would stick to a task for some time and was self motivated. This showed even more when she was put on a special reading scheme as she was behind where she should be for her age and she flew through it, showing great application, but it was on a 1-1 with a sympathetic teacher, who couldn't praise her enough.
We moved her in yr2 private, 18 in the class, as opposed to 31. The change was remarkable and obviously suited her. It took her a good couple of terms settle, but now she is thriving, although is still forgetful and will forget her books, so has a buddy to remind her!
We thought we may have to go down the Ed.Psych. route, or there maybe some other problems, but there obviously isn't. Although a friend who works as a specialist teacher did do a basic assessment and found she is a visual learner and her processing skills were weak, but not awful. She is going to retest this summer, when we visit again.
How is he at home? Would he sit and work with a tutor and remain focused? Do you think there are any issues, apart from what you are being told? If not then I would be tempted to move him if it is an option.