When I was first experimenting with neutrally buoyant/horizontal trim instruction, I did much of my experimentation in refresher classes and pool discover scuba sessions. I discovered that in both cases, once I got the students in the deep end of the pool with a decent idea of buoyancy and trim, I could just get their attention, do something, and signal for them to imitate me. They loved it, and they generally could do whatever I showed them. That included during youth discover scuba birthday parties.Students want to dive JUST like their instructors. If you don't kneel: they won't. If you don't lie on the bottom: they won't either. If you show them how to be neutral and use only your fins: they will emulate.
When I saw that discover scuba students at the end of a 2 hour pool session looked more like experienced divers than the OW students going through two days of pool sessions, I decided it was time to go all the way with the OW students.