srose,
High school seniors is what I do mostly, and I now that telling those kids what clothing to select usually falls on deaf ears. The girls are gonna wear what they want to, then complain about how heavy they look, and the fact their bra straps show, right?

They just do that,, who knows why???!!
As for hair, I do believe you need to try to watch it a bit more carefully, but don't see anything too upsetting about hers. Maybe a little flyaway, but in my part of Texas, and probably yours, many days are windy, some hairspray on your fingers rubbed across the unruly ones will help.
One thins you might work on is the location background. If you can keep that toned down, without so much sunlight behind the subject, I think you will be better off, and watch the hot spots on the skin, as in #3 and #4 especially. Good shallow depth of field in these.
And, as has been mentioned, the posing in 3 is awkward, and cropping in #2. #1 and #3 are, in my opinion the best, but those hot spots need working on.
Always try to stand the subject in complete shade, and try for shade on background also. Get the hands involved, instead of just hanging.

I would also recommend retoucning for this age group.
Allin all, under the cirsumstances... wind and the speed usually required to work, combined with "real" people who have never modeled before, not bad at all.
