1. Many pre-schools are not licensed for children who need diaper changes (hygiene issues). That is why many of them REQUIRE children to be potty-trained. They're not being mean, it's just the licensing issue.
2. I am almost done training DS2 right now (34 months). With DD5, we took the "wait for her to decide" approach. It took 5 months, constantly going back and forth, success then failure, etc. My father came to visit and decided that we were being wimps about it (his words). In 1 day he had her trained. She loves my dad and so followed him around all day long. He made sure she drank a lot of liquids, and every hour he would announce "potty time" and she'd have to go sit on the potty. She was also wearing undies, not pull-ups. Seriously, that did the trick. Now, I'm not discounting the 5 months of preparation we put in, but he finished it off.
Now with DS2, we decided to just go "
cold turkey" based on lots of friends' advice. During the day DS is in undies, at night (and naptime for the time being) he is in pull-ups. I took off on Friday to stay home so we'd have 3 solid days of it. Day 1 - 4 accidents, no successes. Day 2 - 2 accidents, one success. Day 3 - 1 accident, 4 successes! We are now pretty much accident-free. Haven't started working on naptime or nighttime yet, I want to really have the daytime part down first. But we just can't believe we wasted 5 months with DD.
So - my advice is to get some Resolve (carpet cleaner, that is

) and lots of undies. Put him in pants that have elastic at the ankles (to contain the mess!) and socks. This will minimize your mess. We carried around a bag with us for a few weeks loaded with extra pants, shirts, undies, socks and wipes, along with an extra plastic bag to put messy clothes in. Only had to use it twice.
My son never minded a dirty diaper, but he does NOT like dirty undies. 3 days did the trick for us.
Good luck!