The general consensus here is that everyone who tries, gets a BB. So amongst 20 students testing, you might have 2-3 who are really good, 5 who are pretty good, 5 who are so-so, and 2-3 who frankly couldn't do much effectively if push came to shove.
I've never been to a school where they say "you just aren't coordinated enough or athletic enough to get a BB". Consequentely, everyone who shows up gets the BB, at the schools I've seen anyway. It's akin to the high school diploma - sure there's work, but EVERYONE graduates.
I've seen tests like that, and honestly.... they were embarrassing. While everyone is at a different level in terms of physical ability and skill, there needs to be a minimum requirement. Which people should have developed by coming to class regularly for a few years.