The issue is not the validity of school, it is that demonstrating the curvature of the earth can be done with your physical eyes and a little bit of critical thought.

There is no experience —physical or astral — that demonstrates the earth is flat, yet there are abundant verifiable experiences that demonstrate its curvature.

To return to your original question, yes, if you use your astral body anyone can easily verify that the earth is not flat. A beginner can verify that simply by flying straight up from their body and looking.