Personally I would introduce this topic by changing your frame of reference a little bit. Start with stationary objects with a certain wind speed (e.g.: wind blowing around a flagpole). It will be easier for a high school kid (especially one not that interested in physics) to visualize. And then move up to moving objects. Remember if you want to do this intuitively it would be much easier to visualize something like a car or train (simplify the shape of course to a block or cylinder) because then you don't have to include anything about the pressure/density effects as you move higher in the atmosphere. If you have really advanced students then you can move on to the rocket launch scenario. Be warned, I know 3rd year engineering students (for that matter engineering graduates) that have a very difficult time grasping these concepts. But if you really want to know the math behind it, look for an entry-level fluid dynamics textbook.

On another note, my copy of Space Propulsion Analysis and Design gives the following delta-v losses for various rockets (I'm only going to give the gravity and air resistance losses for comparison):

Ariane A-44L: Gravity Loss: 1576 m/s Drag Loss: 135 m/s

Atlas I: Gravity Loss: 1395 m/s Drag Loss: 110 m/s

Delta 7925: Gravity Loss: 1150 m/s Drag Loss: 136 m/s

Shuttle: Gravity Loss: 1222 m/s Drag Loss: 107 m/s

Saturn V: Gravity Loss: 1534 m/s Drag Loss: 40 m/s (!!)

Titan IV/Centaur: Gravity Loss: 1442 m/s Drag Loss: 156 m/s

Now it's plain to see that gravity losses are an order of magnitude higher than drag losses, that is more a trajectory design issue than anything else. Both drag and gravity losses can be mitigated by changing trajectory (gravity losses are based upon the amount of time thrusting directly against gravity rather than orthogonal to it, drag is based on angle of attack). I know this is advance for high school physics, and I've highly simplified the idea. But you have to know the can of worms you're opening by including air resistance in these questions

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