Why did the head teacher call Albert?Why did he feel the medical certificateis burning in his pocket???

The head teacher had summoned Albert in order to ask him to leave the school. The reasons behind expelling Albert was that his presence in the classroom was disruptive of the discipline and decorum expected in a classroom. It created animosity in the class and was a source of distraction for the teacher. It hampered the teacher in his objective of teaching the students and also disturbed the students in their task of learning. Einstein's refusal to cooperate in the class,behave according to the teacher's dictum and being rebellious was obstructive in the way of carrying out work in the classroom.
Albert could feel the medical certificate burning a hole in his pocket because he was going to leave anyway.