Perhaps we are all missing the point here...Did he eat breakfast at all before going to school. Perhaps he's a bit nervous going to school due to something happening in there.
I remember my school days, hated every minute as I was slagged a lot , anyway, I could never eat much in the morning cause of the nerves...Once I got in in I was kinda ok but as a result I cant eat much in the mornings.
Sorry, if I'm off the mark here, only read 3 or 4 of the comments but you never know, specially that age. Get him when he's relaxed and ask him if all is ok in the class. Sometimes it take a few goes b4 they'll tell you. Agian, sorry if everything is ok there. Perhaps hes just changing. As you said better to have a bowl of crap pops than nothing. Mine like the cherios!! And toast. lol.