To put it mildly, Mr. Braithwaite has his work cut out for him with the semi-literate students he is tasked with teaching. Most of them initially have very little interest in learning and even less respect for authority figures such as their teacher. If I had to single out two big disappointments for Mr. Braithwaite, it would be when he receives his first Weekly Reviews and the incident with the burning sanitary napkin.
Weekly Reviews are students' opportunity to write about anything school-related that has made an impression of them during the course of the week. Mr. Braithwaite's disappointment lies in how little they had to say about him. Their submissions proved that they were far more interested in their dance sessions and the local boxing club team than in the new "blackie" teacher. His disappointment here stems from his initial inability to make a difference in the lives of those he is teaching.
The second big disappointment that I will mention is the incident with the sanitary napkin, which takes place in chapter 8. Returning to his classroom during recess, Braithwaite finds a used sanitary napkin which someone had tried to burn in the fireplace grate. Members of his class are standing around treating this as the joke of the century. He handles his disappointment by sending the boys out of the room and explaining to the girls why their behavior was unacceptable. He then leaves the room for five minutes to give them an opportunity to remove the smoldering napkin.