It depends on how much your son needs, service-wise. Worcester tends to offer more in the way of services as they have the population to justify the cost.

I substitute taught in Shrewsbury when my own autistic son was young and in Worcester, and Worcester’s services blew Shrewsbury out of the water. I’ve heard the same for Westborough, and I would be surprised if Northborough and Holden were any different.

That said, if he doesn’t need much in the way of services I’d definitely advise that you look outside the city. I grew up in Westborough and it’s one of the top public school districts in the country.