I'm also a long time lerker first time poster.My daughter 10 had
many obsessions like your son did. Her test scores have always been in the 99 percentile and is a 2nd year magnet student in D54. Her old school is on the same street.(The previous poster will understand)I don't think a subject or grade acceleration would have worked for us simply because dealing with older kids at that time wouldn't of work. I must admit though her second grade teacher helped greatly being a former 5th grade teacher and really knew how to deal with my daughter. Also at the magnet
school all the kids are gifted thus a third grader and a sixth grader get along. I don't think an average third grader is going to appreciate being with a first grader.