Boys are taught Maths in form-groups for the first three years, with extraction lessons operating one period-per-week for the most able. They are then placed by ability in six sets during their fourth and fifth years, as they work towards IGCSE, which is a more challenging course than GCSE and better preparation for both A-levels and the IB.

In the Sixth Form, boys can presently choose either Maths with Statistics or Maths with Mechanics to AS and/or A Level, with Maths traditionally the most popular subject choice. Additionally, there are two Further Maths options, where boys can choose either Pure Maths & Mechanics, or Pure Maths with a mixture of Mechanics, Statistics and Discrete Mathematics.

All KES mathematicians take one of the annual Maths Challenges, and many boys qualify for the ensuing Olympiads. KES also enters teams of boys in various Maths Team Challenge competitions. There is a thriving Maths Breakfast Club for extension work beyond the curriculum and a very active Mathematical Society at KES.