I do home childcare, so I get the whole ratio's thing. Unfortunately that is a center drawback. For those nay-sayers about 2's and even younger being potty trained (someone said the adult was trained not the child, or something like that)...its bull..sorry. You can train a child to tell you when they need to go. I have had 5 living examples in my home childcare in the last year. The youngest was 22 mos, the oldest 28 mos. The most recent just this month, turned 2 on Sept 2, did the method over a 4 day weekend, and has the pee thing totally down pat, has not had one pee accident since. The poo thing we are still working on and he's had 2 of those since we began. His parents are likely using pull ups at night, as night training is different.
These people have done the "3 day potty training method" by Lora Jensen. It does work! You do't take your child at timed intervals, but remind them to tell you when they need to go. Its a potty boot camp for a few days...like waging a little war..but the results are incredible. Yes, they still need assistance with pants and hand washing..but way better than diapers. I support them in this endeavor once they are back to daycare after their long weekend at home. I have yet to have anyone fail or dislike the results of their efforts.
As far as your actual issue with childcare...if you go thru with something like I mention...you need to have the support of the childcare. To do one thing at home, then back to diapers at daycare...very very confusing and I fully believe (in my 20+ years experience with children) that it will confuse him. Discuss with them moving him up early if you can show that he will tell them when he needs to go (but that he will require assistance with pants and handwashing, etc)...come to some agreement if that is a possibility, since its coming in a few short months. Your other options are to find other childcare, or wait it out.
If you can come to an agreement, I urge you to try this method...perhaps your agreement with them if you have him "well trained" they can do a trial day with him where he is telling them he needs to go? (if they even can, due to ages, etc? I am unsure how that works in centers as I do home childcare in MN and those are the rules I know)...
As I have seen repeatedly on this site....it really is hard to change peoples views on something like this....having a potty trained 24 month old is tough for so many to grasp in this day and age...not sure why? So even if you had a trial day with the older class, the staff may really not support his efforts? I would be suspicious if it were a negative outcome, yet at home things were great.
Potty training kids before age 2 1/2 is my mission...not training ME! SO far so good. I currently have 3 Full time'ers in care over age 2...the oldest of which will be 3 later this month. They are all trained during the day for me.
Good luck and let us know what happened!
You can do it!