I'd say doing some sort of testing is probably worth it even if you decide not to try out the schools. It has helped me immeasurably with homeschooling, frankly. I have a much better idea about what DS7 knows and doesn't know, and I have a much better idea about how to teach him--what will work and what will instead frustrate us both.

It can be expensive. That's the big drawback that I can see.

Aside from money, is there any other reason you don't want to test?

Kriston