I believe there is a team in Arizona or Texas(Maybe there's one in both?) that is a middle school team. Then there's a high school team in the same district.
Also there are plenty of teams that are a K-12 school (ie. 330) that allow younger kids on the team, or non-school affiliated teams that allow younger students on the team (1902).
EDIT: The team I was thinking of was team 1484 from Texas.
http://www.thebluealliance.com/team/1484
Unfortunately, it appears that they didn't compete this season.