Rule #1. No relationships between high school and college students. They must stay between one group or the other.
Rule #2. We're serious about rule number one.
Rule #3. Teach the students to do the work. First do it and have them watch. Then equally split the work 50/50. Then sit back and watch the students do the work.
Rule #4. Treat the students with respect, no matter how "dumb" their questions seem. If they are asking questions, it's probably because they want to learn more. Everyone can learn and be productive, it's just that some students learn through different methods or speeds. Be accommodative towards the student, and be patient.
Rule #5. You are a mentor. Act like one whenever the students are around.
Rule #6. The wise learn from their own mistakes. The wiser learn from the mistakes of others. If you need to, step in before the students make a really egregious mistake; like double-checking that the students wired the Victors in the correct direction before they power up the robot for the first time.
Rule #7. Never do anything that a student is capable of doing*. If you have a few students in the shop who know how to use the milling machine, let them mill some parts. (Besides, it often turns out the mentors get plenty of chances to mill/turn parts at 3am after the students went home due to driving/license retrictions, especially in the last week before the ship date.
)
Also, there are some times where due to part complexity and time/material constraints, a mentor is probably better suited to do the job than a student. If the part is so complex that it takes the student four times to get it right, it's probably to have the mentor make the part and bring the student over to explain the process of how they would tackle the problem.
* Unless there is less than three or four days left in the build season and the robot is still far from being completed... There's some leeway here for "all hands on deck" to just get the robot done. It's not very inspiring for the students to ship an unfinished robot.
Now making the transition from high school student to college mentor wasn't that hard for me. I had started to take a leadership position during my last year of high school on 228, and I've been volunteering at FIRST events since 2006. I had already begun to make the mental transition from "being one of the inspired" to being one of the "inspirers" well before I graduated.