First, you need an exercise that is gender and age-appropriate, so evaluate those characteristics first. Second, does your students’ equipment hinder their ability to get “out of the back seat”? If they’re wearing the old rear-entry boots, then there’s no way you’ll succeed. With that, I’ve had some successes by leading students through a drill where they’ll see/feel the benefit of keeping the body forward. While in the more gentle areas of a terrain park, take them over the side of a ramp at moderate to slow speed, without telling them what to look for. Let them discover how the skis tend to slide out forward from under them as they either get a little air, or try to keep the skis from leaving the snow surface. Watch for facial reactions to see if they’re caught by surprise, etc. Pull to the side, discuss it with them/ask what they felt, then try a second pass and have them focus on keeping the tips firmly on the snow as they go over the crest of the side of the ramp/ridge. They should feel oveall more stability and realize the immediate benefit of staying forward. Once they get that connection, have them focus on keeping their feet “tucked underneath”; it’s more of a mental than physical thing, but if they keep only that in their heads and try to just enjoy the ride, they should start to take ownership of the concept. Good luck!