Class 1 Fluids: Oil, Transmission, differentials, Transfer case (if applicable). Have them all climb under and point to both the drain and fill plugs. Even better if you serviced a rear diff or something as part of the class. Bring examples of each kind of oil and show them how to find the oil specification in their owners manual. Also bring in various vehicles (preferable a mix of FWD, 4WD, RWD cars and have them point out where the oil filter is on each car. Don't forget to find a car with an in-line oil filter in the cab. vs. one on the block underneath. Air filter can be tossed into the class also. While servicing the rear diff, explain front/rear driveshaft, show them zirc fittings on serviceable u-joints and ball joints, and have the kids properly grease the joints while doing the diff service. Teach them how to clean spills, reclaim and recycle the used oil.

Class 2 Electrical Troubleshooting: Go over fuel injection and the basic car electrical system. Preferably, how to use the owners manual to find the fuse box, replace, and determine if fuses are busted. Bonus points if you have some blown fuses and put them in certain components of your car and make them troubleshoot to find why it won't start or the 12V outlet won't work. Explain the problem with putting in undersized fuses (this is easy, just put a 5A in a 12V socket and overload it.) But more importantly, explain the dangers of putting too large a fuse in an area...it can cause a fire. This is where you go through the spark plugs, fuel delivery system, etc. Make them point out the coils spark plugs, wires, etc. Bonus if you can get an older car there and have them identify the difference between coil over and distributor/points system. Even better if you have a classic carb. vehicle there at the same time. This is also a good time to discuss air delivery into the engine, mass airflow sensors, etc. Don't forget the exhaust with O2s, fuel pumps. Air filter can be discussed here if you didn't have time in class 1. Extra Bonus: Take a bit to explain fuel octane, what it does to the combustion process, engine timing advance and retard. That you are wasting $$ putting premium into a vehicle not designed for it, but likewise could be destroying a motor with pinging and predetonation if you use low octane on one designed for premium.

Class 3 Auxillary systems: I'd focus on cooling systems. In my experience this is the #1 failure of older vehicles and killer of motors. Explain engine temp, why it's important. Point out the radiator, thermostat, water pump. This is a great time to point out serpentine belt service, fan clutch. Teach them each auxillary equipment bolted to the engine: Power steering, AC compressor, alternator, etc. As part of the practical part of this class, have them drain a radiator and deal with the antifreeze. Teach them to properly refill and burp the system. Antifreeze corrosion inhibitors are only good for 5-6 years, teach them how your water pump can corrode and fail if antifreeze isn't changed. It will be easy to find a vehicle that needs it's antifreeze changed to do this, and the kids will see the visual difference in quality when you dump the crappy stuff out. If the vehicle has decent access, make sure you have them put on/off the serpentine belts, this may involves removing the fan from the fan clutch, which is a good lesson also. Bonus if you have an OBDII reader and can show them the vehicles running temperature. Teach them how to properly fill it so there is no air-bubbles which can destroy the system. Preferably using the bleed screw on the upper radiator hose, or raising the front wheels when filling. Have them check the hose quality and identify all the hoses (back to the heater core, etc).

I forgot tire changing. You should fit that in somewhere too, or do that another day as it's own class.

That's how I'd do a 3 day crash course.