We have had the same problem for about two years. Our pediatrician said "you can put him on meds but the side effects will likely be worse than the terrors."
Some things that worked for us and have helped bring it down to maybe once a week at most-
High protein snack right before bed
A cool room with a fan blowing directly on him
Loose fitting PJs and no tight blankets or sheets
Giving him a warm relaxing bath right before bed with no talk about school or anything stressful.
Waking him up 2 hours after he goes to bed, just enough to stir. This seems to disrupt the sleep cycle enough.
