I am a high school math teacher and go though a short series with my students. I do short segments when we finish lessons really early, or get ahead of the other classes, etc. Here's how I approach it.
Always the first lesson: How to know when you can retire...
step 1: explain to them how over the long haul, the stock market has shown to be the best return on investment, at 7-9 percent historically.
step 2: explain how the trinity study shows that if you have your money in the stock market, you can pretty much take out 4% of that amount without running out.
step 3: explain that once you get enough money in there to live off that 4%, you don't need a job anymore...ever.
step 4: explain how 4% is 1/25 of 100%, so working in reverse, you just have to take your spending level, times it by 25, and that tells you how much you need to be able to retire.
step 5: I work them through a couple scenarios...
Person 1: makes 100k/year, spends 90k. This person can save 10k per year, and needs 2,250,000 to retire. This person will appear to be quite rich, but is not. They will work forever.
Person 2: makes 80k/year, spends 40k. This person can save 40k per year, and needs 1,000,000. This person will not look rich, but will be a millionaire quickly, and will be retired when he/she is relatively young.
step 6: reiterate that FI is the moment when your investments reach that tipping point, where your money makes more money than you spend, and you can wake up and say "what do I want to do today", and then just go do that thing.
At this point, I ask the class to think about whether there is an age when they might want to be FI. I ask them to pick an age just so they can play around a bit, and then to start playing with the numbers for how much they might earn and spend, and see if they can make the math work out to retire at their desired age. For example if they think it'll be a priority for them to spend X amount, then I ask them to figure out how much they'll have to make to be able to save enough to retire by that age. Or if they want to have a particular job that pays x amount, I ask them to think about how low they'll have to get their spending down to have that job and still be able to retire at a particular age. Basically I want them to start thinking about how spending, earning, and your FI age are all interrelated as well as manipulatable.
At some point in the discussion, a student always asks me what my FI goals are. I am totally transparent. I tell them that I'm 33 and my wife is 32, that we grossed about 140k in the last 12 months, and that we saved about 70k of it. That our goal is to be FI at a little over 40, and that we are on track to do it. That we spend far, far less than most people around us, and that we are very happy knowing that we will be FI in not too many years. That that's why they often see me biking to school, and why I drive one of the oldest cars in the staff lot. And that if they'd like, I'll share some things my wife and I do to keep our spending down really low, but to still enjoy a fantastic life together. This hooks them in for subsequent lessons. Here's some of the lessons I do later:
1. How to spend waaay less than most on food and still eat great.
2. The most efficient way to buy a car and minimize the total cost of ownership (depreciation/insurance/gas/repairs)
3. How I get free airfare and hotels anytime I want (I explain travel hacking...but my real ulterior motive on this is to get them excited about earning a high credit score, and hooking them into wanting me to teach them how a credit score is calculated. My thought is that this will give them a cool way to understand the importance of good credit at a young age)
4. What are index funds, Roth IRA's and 401K's, and how do smart people use them together to build wealth.
Good luck with your presentation, this is such an important topic to be sharing with young people.