Discrimination/Divided Class Systems
Neil is bullied in his school because he has of a lower social status. In fact, his mother is glad that he has gotten into a prestigious school which rich students attend, probably because she wants to elevate her own social status as she can brag that her son has good manners and goes to an elite school.
Neil thinks so little of himself that he, in desperation, makes up an outrageous excuse to not go swimming so that he will not have to reveal his skin disease to Michael’s family as he is certain that they will feel disgusted and Michael will not want to be his friend anymore. He is so simple-minded to think that everyone will judge him based on the outside only.