The definition of Team in the VRC Tower Takeover Game Manual is as follows:
Team - One or more Students make up a Team. A Team is classified as a middle school Team if all members are Middle School Students. A Team is classified as a high school Team if any of its members are High School Students, or made up of Middle School Students who declare themselves “playing up” as High School Students by registering their team as a High School Team. Once declared and playing as a High School Team, that team may not change back to a Middle School Team for the remainder of the season. Teams may be associated with schools, community/youth organizations, or a group of neighborhood Students.
There is no limit to the number of Students that make up a legal Team.