Although the book nor the play never specify, we assume that Christopher is neurodivergent.  Someone who is neurodivergent behaves, thinks and learns differently compared to those who are neurotypical. This term can be used to describe an individual whose brain functions differently to what we consider “normal”. This includes people with autism, ADHD, Tourette’s, dyslexia and a range of other neurodiverse conditions. Most likely, Christopher is on the spectrum, meaning that he has the characteristics of an individual with autistic spectrum disorder.