mobile

Hi, I have a question about the unique identifiers that are transmitted to a network by an android device. So, basically my schools wifi network blocks all mobile devices (android, iphones) but it works on laptops. Authentication is done through 802.1x and everyone is assigned their own username and password. When they started blocking phones I thought that they detected them through MAC addresses or hostnames but I was wrong. Does anyone know how they can differentiate between laptops and mobile devices?