i believe the aamc collects this information, although I don't know that it is accessible. For example, the US News rankings don't use this information, even though it would be a good barometer of med school placement.
You shouldn't be worried about that and you should be doing your research.
But honestly, it's the individual person who makes the board scores, not the school. I would be more focused on the schools curriculum and if you can learn in it than the board scores. I know that is very hard to do as a pre-med, but that is what I would reccommend.