I "think" some schools have a policy about testing too far out of grade level. That is, I think in some districts there is a ceiling that the tester won't go beyond. I don't know if this is the case for your district, but it could explain the reluctance.

I think the issue for the schools is twofold:

1. the time involved in testing kids to their "true" capability.
2. thematically difficult materials at the higher grades (i.e. age inappropriate text).

I would certainly ask for a conference.