Just so you know - you are not alone! We are having issues with our kindergarten as well. Weekends are getting better & we have had 2 good days this week. It is a big routen change... I'm hoping once he get a little more use to the change it will get better.
We haven't taken anything away, but we do rewards (usually candy) at the end of the day (right before they brush their teeth)... if he does poopoo his pants he dosen't get his. And he doesn't like his siblings getting the reward and him not. So, I think that is also helping a little.
Also, we make him clean himself up when he does it. Which I think he is starting to figure out it takes less time to just go potty in to toliet then it does to clean up the mess he has made of himself.
Now, if he lies about it when we smell it... he does get punished for lieing - which is usually a time out.
Not sure if this is your only child or not, but if you do have more then one... try to reward for other kids at the end of the day and her only if she stays clean & see if it helps. With Halloween near, candy is in nice sized treat/reward size bags & a lot of stores have the fun size bags on sale. We have a treat bowl they get to pick out of... right now it has Skittles, Gummies, and other fruity flavored candy - my kids favorits!
Good luck!!!