If everyone says that this was a playful thing (and it was a playful thing, not a cover up?), my first instinct is that there's something medical going on:
- alopecia
- ringworm
- thallium poisoning (or other, but we had a thallium case at my sister's school recently)
- thyroid
- reaction to medication
- etc. etc. etc.
Of course, my 2nd reaction is a prank:
- nair
- glue
- etc.
::blushing:: Gawd...I hadn't thought about it in years, but something we would frequently do in the USMC, was put Nair in the conditioner bottle (men only!!! too cruel, to even contemplate for a girl). Low, and behold, our friend would slowly (or quickly!) start to lose their hair. It was something done in fun, the first person who "broke" and laughed would have to pay for the night out for everyone involved -of course including our bald friend- ... Other times we would write something in our friends hair while they slept. When & where we were doing it, it was fun and fairly harmless, since the boys are all nearly bald anyway (albeit testonery & prankish), but I've heard of other's doing it on accident, or to be mean. Certain other chemicals when applied to hair would also make it fall out. It's possible your son's friend has had one of these things happen to him also. Either at school or at home.