Open book test? That only works if you can read.
Our home schooled daughter took the SATs a few weeks after turning 13 (she was not in HS yet) & then ranked in the 86th percentile of “college bound” high school students. This was in 1997. She said that something was wrong if she was that much better than all these other kids that had already had 3 years of HS and were supposedly college material.
I told her the truth. That she was indeed smart & educated. At the same time, most of them were severely lacking in real education, that they had been cheated and lied to by the school system. I also told her that she had an obligation to herself to make the most of her skills. She has.
Home schooled first granddaughter had a similar experience a few years later. Sarah is technically a high school senior today as she is enrolled in a second year of college.