As per the above post, my sugars sometimes rise if I exercise, particularly if my levels are a little higher than normal.
I was diagnosed age 7. My sugars were sometimes a little unpredictable as I was growing. My doctor said it can happen if experiencing a growth spurt.
Alternatively, he could be coming down with an infection. This will raise blood sugars.
How long has he been diabetic? If it was quite recently he could be coming out of the honeymoon period and his insulin requirements are increasing.
Finally, maybe he has had something to eat (perhaps something he shouldn't) and doesn't want to tell you? When I was that age I understood I had diabetes and that I had to keep my levels between x and y. I did struggle, however, to fully comprehend the importance of good control. When my friends would have biscuits or cakes it was hard to say no. You say his sugars are highest at 4, which would be just after school. Just a suggestion...
Anyway, hope you get things sorted soon.
Take care
Emma