Hacked my school wi-fi , i want to make its security better

Greetings Everyone… So Im just beginning with pentesting… but the other day i was at school and i hacked into my schools network. i then noticed it had a login page which asked for a voucher code. I proceeded to randomly type numbers but it didnt work… after doing this i proceeded to make a scan of the network. i then got mac addresses of device`s on the network and decided to try changing my mac address to one of those… so this worked. i got complete access to the network… i was wondering what other different measures they are to restrict the access of devices on a network apart from their mac address… would be great to hear what you guys think…

Only if you have access to the router admin page, 192.168.1.1 or something similar, then you will be able to set a DHCP rules to filter any Mac address that is not assigned to the router.