We tend to break things down by function:

Programming
Electrical
Vehicle - the part that gets us around the field
Manipulator - the part that does stuff when we get where we're going
Compliance - Keeps track of weight and other rule compliance

During fab any student who is standing around may be drafted by any team to help with what they're doing.

We also have administrative/fundraising teams. These are broken down differently and the organization there changes from year to year depending on our fundraising activities. Each student is a member of at least one technical team and at least one administrative team. Students that have been around two or three years can be student lead for a team. Each team also has an adult mentor.

It may sound silly but the Compliance team is probably our most important technical team. We weigh every part before it's installed, including fasteners. Since we started doing this our estimated weights have never been more than 1 lb. off our official weight. Also before a part is built or installed we have to show how it complies with the rules. So we've never had to change a critical component because it was made out of something not legal either.

It may not be the best way, but it works for us