By 1970, Kesteven County Council announced plans to turn its grammar schools into co-educational comprehensives for ages of 11–16 and leave Grantham College as the town's only sixth form.

Other parts of Kesteven became comprehensive but responsibility for education passed to Lincolnshire County Council under the Local Government Act 1972, and King's remained a grammar school.

[2] On 1 August 2011 The King's School ended its long relationship with the local elected authorities and the town of Grantham, by converting to a selective academy.

[3] Boys attending the school are provided with opportunities to partake in extra-curriculum and academic experiences such as in sports, music, art, drama, chess, the Duke of Edinburgh award scheme and languages.

Subjects offered by the school include Art, Business, Computing, Drama, English, French, History, Music, Physical Education (PE), Politics, Religious Education (RE), Biology, Chemistry, Design and Technology, Economics, Financial Studies, Geography, Mathematics, Physics, Psychology, Science and PSHE Curriculum.

An Office for Standards in Education, Children's Services and Skills (Ofsted) inspection in May 2008 graded The King's School as "outstanding".

The majority of students go on to higher education following the completion of their A-levels at the end of Year Thirteen (aged 17–18), and it is common for several boys to gain Oxbridge offers.