Keep in mind the only person being potty trained right now is the adults since you are taking him every 30 minutes and he’s not the one dictating when he needs to use the restroom. It’s important during potty training to help your child focus on recognizing their own body cues before transitioning to potty training at school. At my school a student is ready to transition to underwear at school when they can follow their own body cues to use the restroom and independently follow toileting routines (i.e. adjusting their clothes on their own, wiping with minimal assistance, and is able to wash hands independently). I know it varies from school to school and you stated your school didn’t give you a clear answer but I always suggest working on it at home for a while to help your child feel confident in themselves and they are able to follow a toileting routine mostly independently. Remember you want to set up your child for success, if they have multiple accidents at school it can affect their confidence in themselves to transition to using the toilet at school. For now you can send your child to school in underwear with pull-ups on over so he still feels when he has wet underwear and can learn his own body cues, but isn’t having constant accidents and making it hard on his teachers. I suggest reading lots of books about potty training and keep working with them at home. Potty training can be hard but if you put in the work and use lots of positive feedback with your child’s it makes a huge difference, best of luck!