I recommend checking back in with your doctor as there could be an underlying issue as some suffer bladder issues.
Also - the kids laughing at him for one will indeed cause him undo stress. No one wants to be made fun of at any age or be disrespected.
My next question:
What has changed in your home or his school? Just know that it does not have to be huge to make an impact on a child.
My son also reverted in his potty training ways and the trigger was events at school.
There was an issue of not being able to have a permanent teacher. This turn-over before settling caused not just my son, but a few of the kids in the class to have accidents and revert on potty training.
My S-I-L decided to redo her kitchen: new floor, repainted the whole thing and new counters. This impacted my nephew to revert and do the same thing as your son.
Many parents tend to forget or do not realize that small stresses like this can affect their child. If they are used to a routine and it is changed, be prepared for the repercussions of that.
With my son, I always talk to him about things before we do them and include him to the best of our abilities so he feels like he has some control in our family. I am sure some others may not agree to this, but as I deal with stress as my job, I would rather avoid affecting my son. Plus, he enjoys it as he feels 'grown up'.
Another tool to find out issues: use a puppet or a beloved stuffed animal and have a conversation with your child. It works wonders! My son will grab his frog, bunny or ask me to dress up as character to chat about all things to vent and unload. (I even have a doll that my son calls 'mini mom' as it looks somewhat like me.)
This is one of the BEST things we have discovered and we have been using it successfully for over two years with our son. Whatever is bothering him will spill out to these inanimate objects - even tho he knows darn well we are the ones that he is really talking to right now. But his imagination takes over, as does the built-up emotions.
If it truly is due to being busy - then what I did, was have a potty break every hour and a reward system. But I still recommend you have your bases covered and research the issue as something could be stemming the problem.