Just because you're allowed access to the school's network, via a school provided account/PC, doesn't mean you are allowed access via your "personal device". Some entities make stiplulations in that regard. Even if you have a "certificate", if they are using MAC filtering, you will still not be able to access their network, using an unlisted device. Good luck with that, and don't be mad if you get in trouble.
No, I suppose it's specific for your school. So its probably different. Mine for example is "0758899@hro.nl". If you dont know you should ask those men behind computers on your school .