When doing this demo for grade 12 physics students and for university students I used something called the Smart Pulley to gather experimental data to back up the theory. The Smart Pulley is a pulley wheel attached to a photogate that you can buy from PASCO. The photogate is connected to a computer with special software so that the position of the rocket can be measured. This is done by wrapping some fishing line around the pulley wheel and attaching the other end to the rocket. The wheel generally holds about 4-5m of line. This will give you the first 2 seconds of the launch, which is the powered phase of the engine. The software then lets you graph position, velocity, and acceleration vs. time. The results can be shown to the students. The effect of the tension of the line is negligible when calculated but the added weight of the line should be added into all calculations.
The other quantity to measure is the final hight of the rocket. To do this I used 2 theodolytes as tracking stations. Doing some simple geometry yields the height of the rocket from the 2 angles the theodolytes measure and the distance between them. This measurement is pretty good for accuracy.
So there you go. That's the demo. Try it yourself and have some fun. Starting rocket kits can be bought at most hobby stores for about $45. Enjoy!