How young is the son? You are not tellin anything bout it.Kindergarten,elementary grade or high school?
For some pre-schooler,it's just normal to them in the beginning to be scared especially they were not being taught the need why everyone needs to go to school..For a pre-schooler,mother should give them company in the school for few days in the school coz some were experiencing anxiety to strangers giving them assurance that you are just outside the classrum in times they need anything.Following days,just drop them in the school tellin them that teachers are there for them always attend to them that you gave them your mobile number so that they can reach you at ease if problems arises...these were not enough but somehow can help u guys..