You are right about the injuries at the high school level.
I wish that I had let the kids run easy long distances early in the season. Instead of hard interval training I would have had them do short speed work at paces they could handle. Later on in the season you may be able to do some short interval sessions.
There are successful programs that go to state every year and all they do is jog all season. They might play some chasing games and the top kids might do some fartlek. This is hard for some coaches to believe, but it is true.
10 x 400 in 65 is not how you win at the high school level, unless you have an established program.