The only catch to the above is if your child needs to test with accommodations for a disability-- in that case, there may be additional information needed and the age/grade thing might come up (it doesn't have to, of course-- it's just that in that case a student who is not homeschooled is supposed to involve a school counselor, which is awkward outside of a high school setting).

Schrödinger's cat walks into a bar. And doesn't.