Its hard with children ...
I am assuming you know how to carb count and to match the insulin to give. However, are you conversant with bolus ratio's and changing them?
Adults would be advised to basal test or to leave 5 hours clear bewteen meals to check whether its the bolus or basal doses that are incorrect.
I would really contact your DSN tomorrow... It may well be that your son needs different ratio's for weekdays at school than when he is on holiday or weekends...