Several things. Follow advice to see child psychologist & psychiatrist. Ask school counsellor about bullying or other precipitating event & ask for teacher reports of behavior change. See your pediatrician with your child. Give date of onset, school reports, report cards & any reason your child might worry about parents/siblings. Don't allow child to stay home. Allow psych md & phd to talk to school re : an iep.
School Phobia. You must have your child see a licensed psychologist with experience in school problems. He or she might also recommend you take your child for a medication consultation.
Again diet! School phobia is not a psychological problem. It is a biochemical one where the child becomes much too stress prone. He/she may have other symptoms such as sound sensitivity. That is why the headache or abdominal pain disappears when the child gets home. I have been able to help many such kids by correction of diet and a few vitamin supplements.