As the story is narrated from the perspective of a mathematically-gifted autistic teenager, the style reflects this experience. The descriptions are often straightforward and factual, though when he becomes involved in a particular idea or is describing a stressful experience the writing becomes more convoluted, with long run-on sentences to indicate the excess of sensory or intellectual stimuli that he cannot fully process. To help keep his ideas clear, Christopher makes certain orthographic decisions - bolds, italics, capitalizations - to make a particular word or phrase stand out, thus making their importance more apparent to the reader.
To help convey the unique perspective of Christopher, the novel is often unbalanced in how it presents details of the world. Expectations of what belongs in a narrative are often re-prioritized to fit his understanding of the world. Sometimes this is done by omission: for example, Christopher is not able to always gauge a person's emotion (including his own), so sometimes he will not mention this and thus the dramatic effect of a moment is underplayed.
Other times the unexpected comes through the addition of elements that seem outside of the narrative: details that seem superfluous to the reader but which are deemed worth mentioning by Christopher. Some of it reflect the immediate concerns of any student, while others are elaborate mathematical or scientific ideas, or even word meanings and narrative definitions. There are whole chapters devoted to a specific mathematical problem or some other cultural reference, such as the plot of The Hound of the Baskervilles. These help create a sense of how Christopher understands the world, the way he uses maths and logic and mystery novels to better cope with the difficulties of coping with life's complexities.
The nature of Christopher's seemingly tangential details is best contrasted to passages where Christopher purposefully includes "descriptions" as per Siobhan's suggestions. Told that such details would be of interest to readers, they actually do not particularly concern Christopher the way his maths and Holmes does. Thus, these descriptions in particular seem out of place and disrupt the feel story, more so than Christopher's chosen tangents, precisely because they don't accurately reflect his own concerns.
Diagrams and drawings appear throughout the narrative - sometimes to illustrate a scientific observation, other times just to see what a picture is like. This shows the limitations of written language for Christopher, and his need to convey ideas in as full a manner as possible.