I find that keeping students close to the bottom for this is very helpful, for it gives them instant feedback on their body position.True story Pete!
I was lucky that my rig trimmed out really well so we worked on my pathetic propulsion. I had vector issues when trying to frog kick. Hugging the bottom kept me form dropping my knees or bending at the waist or whatever was messing with my attempts.
Only took maybe 10 minutes to start to feel some ability to create some thrust.