There are some good summer programs in the Philadelphia area. Some are pricey, some not. I didn't mean to say that there aren't any options before 5th grade. Are there other kids like him at his private school? If not, have you considered other private schools? Philadelphia Magazine publishes a summary chart of private school stats. While the classroom work probably won't be up to his level at any school, there will be other kids like him at some schools.
Is the current school a K-12 school? If so, do you know how many NMSF there are each year? It isn't a perfect indicator, but if a good percentage of the senior class students are semi-finalists or commended, you'll know that there are other gifted kids in the school.
