Not to start a holy war (or keep it going), but I kind of agree with Greenman. I fully expect underclassmen to need some time to develop (my own kid was one), and applaud runners who are running with slower runners to help them achieve their best, but by the time they are seniors would think they would extend the effort (appropriate for their ability) to run well.
I think almost all of the really good coaches appreciate a PR by even their slowest runners as much as by the top guys. Conversely I would expect most good coaches to be disappointed to some degree when anyone (group 1 or group 6) chooses not to race to his ability.
If there is truly no desire to extend that effort in races, excuse them from the races. Just let them practice and be part of the team that way.
My two cents worth (and worth exactly that).