Respectfully, you can't really achieve any semblance of buoyancy control without getting trim down first and you prove my contention that most don't understand the correlation. I call being horizontal the "Scuba position" and other than mask clearing in shallows, it's the first skill I introduce. Not getting it first dooms the new diver to a hundred or more dives trying to figure out their buoyancy. Get it done first, and then teach the entire course with flat trim and neutral and your students look like rock stars when you're done. It's all about comfort, and a trim and neutral student is far, far more comfortable because they are in control all the time. If they're in control from the beginning, then you spend no time trying to keep them from floating away and they learn, far, far faster. In other words, there's a bit of a time penalty early on, but you make it up as the class continues.
Students that are in control do everything more easily and with less drama... and that includes ascending.
The class I did my open water and advanced was horrible (different places). I didn't know how bad at the time. It took me a long time to get my weights where they should be rather than over. Over 100 dives and much more classes later and I'm still learning new things, things that I feel should have taught or at least introduced during my open water class or at least I would have gotten them a lot sooner had I started training right from the beginning.
I was doing play time pool work on sunday and I overheard a instructor tell his open water class that to get certified they had to master flutter kick, frog kick, trim and show the beginnings of bouyancy control. ( I also know they do not over weight there students) I told the owner it is good to see a TIR (teaching it right)