I have been potty training my little girl since she was 21 months. Although she has been successful, off and on during that time, she has just now been potty trained with only a few accidents. She is now 2 and a half. We probably could have accomplished this earlier but frankly both of us got a little lazy. So, here is what I recently did to 'step up the process'. I brought the potty chair from the bathroom to the living room. She is big into Dora right now and loves Elmo, so we bought some Dora and Elmo panties that she had a choice to pick at the store. I remind her every two hours to go potty, unless she has just eaten or woken up from a nap/bedtime. We go 30 minutes after eating and right away after naps/bedtime. You will probably want to start at one hour intervals, or less for the first few hours. Use a kitchen timer, or even a small watch that your son can be in charge of. The alarm will be a cue for him to sit on the potty and you can make a game out of it. You will want to stay as close to home as possible during the weekend. If you can choose a 3-day weekend, that would be even better. However, we all know that we can't necessarily stay home the whole time, so I put my daughter on the potty before we leave home and then the potty chair goes with us in the back of my SUV. That way, I can never be caught somewhere without a potty. It worked great for us. We can go places and although she has had a couple of accidents, especially the first two days, she did remarkably well and quickly learned that she didn't want to potty on Elmo or Dora. There will be some messes, so be patient and let your son know you love him by telling him "we'll do better next time and remember to run to the potty when we have to go". Keeping the potty in the living room where we play most of the time, keeps it top of mind for me and for my daughter. Now we don't have to do that anymore. She runs to the bathroom herself and even reminds me when she has to go during swimming. I expect there will be accidents now and again, but she is even staying dry during the night. Now, if daycare won't let you bring him in underwear, then here is a trick for you - put a pullup over the underwear so he can still feel very wet, but the mess won't be on the daycare floor. Make sure you bring plenty of extra pullups and underwear for school.
Good luck!
L.