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. Boys in the top sets are also prepared for a second IGCSE in "Further Pure Maths".
In the Upper School, boys have to choose one of the three Maths courses in Strand 5 of the IB curriculum; at Higher Level, for those boys with serious future plans in mathematical, scientific or economic areas; at Standard Level, for those wanting Maths as a support subject; or the second SL course called ‘Mathematical Studies', which is for those with no further mathematical career needs as well as those who have previously struggled with the subject.
Nearly all KES boys sit one of the annual Maths Challenge papers each year, with many boys qualifying 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.