I live in the same general area. We had our DS tested at 3.5 and I don't know that it provided much benefit in how the school responded to him. They listened of course but they also did their own evaluation and put more stock into that.
As the others said, a portfolio of of work seemed more persuasive in the end.
If you're in PA, although the gifted programs start later, grade 2 or 3, you can still request an individualized gifted education program for your child and the school district is obligated to respond. This is via Chapter 16: Special Education for Gifted Children.
It applies as soon as you are enrolled in a public school, including kindergarten. So you can enroll in the summer and make your request soon after that. I can't speak to how good/effective it is because we went private. But it's worth knowing because most of the public schools only tell you about the formal program that starts later.
If you're in NJ, I don't have any information about them.
