many years ago I used to do one wetsuit dive, once a year, to remember what I was doing to my students... After about the 3rd year, I rounded up a few extra drysuits, added a couple pool sessions and voila! drysuit diving openwater students!
I found that the retention and comprehension of things that baby divers see underwater is increased greatly by them not being c-c-c-c-c-cold. its one thing maybe if you are a warmy and have your own special wetsuit, totally another if you are in a well used, ill fitting store rental.... (the stores do the best they can)
A good bit of the skills dive for your checkout is sitting their waiting for the instructor to run other students through the drills... as you can imagine, this can get chilly.
Like most, I started in a wetsuit, I made it to approximately dive 40 before switching over to a cheap neoprene drysuit. This just happened to be during my OW2 class, where we were doing 3 dives a day, 1 deeper, one drift, and one night... After the 3rd dive, I was so cold I couldn't get self out of wetsuit. I bought drysuit the next day and never went back to diving wetsuit.
I am a coldy, I haven't dove a wetsuit in easily 12+ years.
just my .02