M.O.
JB,
I agree that you should be up front with the school staff. Although I'm sure they've seen it all, I'd hate to be "that parent" that lies about potty training, only to create a big hassle for them when they have so many other kids to deal with. I don't think anyone expects your son to be perfect, but if he's wetting himself daily or needing to be reminded all the time to be successful, then I don't think that's what schools would call "potty trained". Sure, I think WE do as Moms. But would you like 15 other kids over at your house for a party with no mom's there who were "potty trained" like your son is??? Just pointing out that creates A LOT of extra work for already overworked teachers.
As far as what you can do for your son, what about "naked time". We did summer potty training with our kids. I intentionally kept them outside, loaded them up with fluids and we only wore bathing suits or cloth underpants or shorts with elastic with no underpants. I kept the potty chair on the deck (in the shade and out of neighbor's sights). This made potty training a breeze. My kids HATED being wet and clean up was simple - just hose them down. They quickly get the idea that "if I just pee in my pants" it's yucky, runs down their legs and overall just feels gross. Every time they went on the potty (without having to be reminded or told), they "won" a sucker, Popsicle, etc. Personally, I think the "naked time" approach is phenomenal - especially for those reluctant to go on their own all the time.
Good luck.