100% student designed, while impossible to actually attain*, and 100% student built are goals to work towards. But those students better be 100% mentored.
Jstack's example is a really good one: The students initiate, and learn along the way. I've been on teams where the team (students, mentors, and parents if any happen to be around) does everything, which may be an even more ideal team.
One quick thing I think needs to be said: I've seen a few posts making comments about mentors "doing all the work" in the pits lately. If your only observation of the team is glimpses into their pit at random times during a regional, you don't know whether the students were all on lunch break, at a strategy meeting, or shoved out of the way by the mentors. I'm not going to say that that sort of team doesn't exist. But what I am going to say is, unless you've watched the mentors actively shoving students out of the way, and keeping them away from the robot, consistently, then you may want to keep those observations to yourself or a trusted friend or two. The #1 fastest way to start a flame war on CD is to, based on random glimpses of only mentors working on a powerhouse team's robot, accuse that team of being mentor-designed and mentor-built. It's happened, multiple times. And the normal responses are: "It's not illegal", "It's up to the team how the Inspiration happens", and (this one is usually from the team in question, or a team close to them) "You don't know what you're talking about."
*If you're using the cRIO and the KOP motors and similar required items, those were not designed by students. At least, not by high school students--I might be willing to believe a P.E. working on a Master's or Ph.D., which would count as a college student.

__________________
Past teams:
2003-2007: FRC0330 BeachBots
2008: FRC1135 Shmoebotics
2012: FRC4046 Schroedinger's Dragons
"Rockets are tricky..."--Elon Musk
