Don't make the same mistake I did in the fall.
For a Middle School girls team, I ordered a mix of Youth Large and Adult Small.
Since most of these girls were U12/U13 (6th and 7th grade) I thought that would be fine.
Upon handing them out at a training session just days before a tournament, I quickly realized I underestimated the height and size of some of the players.
I had to rush off to Dicks and grab a few Adult M and even one Adult L to provide adequate sizing. Of course these weren't an exact match but I got close enough, but still poor showing from coach.

Bottom line I would suggets an even mix of Adult Small and Adult Medium (and a Large if you feel appropriate). Or better yet, ask a team mom.