That seems like a good offer from the school and I'd take them up on it if I were in your shoes.

Have you read Misdiagnosis And Dual Diagnoses Of Gifted Children And Adults by Webb et al? It may be worth calling the doctors on the list to see if they're familiar with it. If he isn't diagnosed with Aspergers, a psychologist who works with gifted children should be able to include other recommendations in a report for the school (i.e. more challenging work without another grade skip?).