I would call it "why we need classes in rebellion" or something (to get their attention) and then talk about the Milgram obedience experiment and Asch's conformity experiment. Two classic results that demonstrate the power of authority and peer pressure.
Then get your audience talking about how to foster independence without going too far in the other direction. E.g. teachers who nearly always teach the core curriculum, but once in a while throw out a huge whopper to test if you're paying attention. (This works btw. I had a history teacher who tested our credulity by telling us that the pseudo-documentary Punishment Park was real. I googled it and called him a liar next class, and he gave me an A. The vivid memory of being terrified but right was useful for a few years)
My school has a weekly event on Thursdays where someone can give a 15-25 minute lecture about a topic of their choice during the lunch break. The standard attendance is about 20-30, aged between 14 and 18, and some teachers drop by if the topic is related to their subject. It's heavily interlinked with the philosophy department, in that topics are typically about religion or ethics, so the audience is generally more philosophically informed than average. A good percentage are theists or deists, and there's a very high chance that the subject will be more thoroughly discussed in the philosophy club the day after.
In a previous lecture a few months ago I tried to explain some standard biases, the Map/Territory concepts, Bayes, and generally attempted to compress the core sequences into 25 minutes, which despite a lot of interest from the head of the philosophy department, didn't go as well as I'd hoped for the rest of the audience. The problem was that I tried to close too many inferential gaps in too many areas in too short a timespan, so for this I thought I should take one rationality idea and go into detail. The problem is I don't know which one to choose for maximum impact. I've decided against cryonics because I don't feel confident that I know enough about it.
So what do you think I should talk about for maximum sanity-waterline-raising impact?