In 2023, the school received a "well above average" Progress 8 score; 90% of pupils achieved English and mathematics GCSEs at grade 5 or above, which was far higher than the national figure.

"[14] The problem was solved in 1901, when a syndicate of local gentlemen and businessmen launched a venture to establish a school for girls on a private basis.

[32] To meet these requirements, the county council drew up a scheme for providing secondary education across its jurisdiction in August 1918 and decided to take over the running of the school and purchase its premises.

[41] Early plans envisaged the school being rebuilt at Westholme, parkland owned by the county council off Westgate, but this never came to fruition.

[45] In 1956, the school acquired the disused and mostly dilapidated offices of Sleaford Urban District Council on Jermyn Street, adjoining their Southgate site.

[49] The educational opportunities for secondary modern pupils were limited compared to those at grammar schools, prompting criticism of the tripartite system.

[50][51] A reluctance to improve secondary moderns or expand grammar schools under the Conservatives prompted the Labour Government to issue Circular 10/65 in 1965, which requested local education authorities convert to a comprehensive system.

[56] Despite support from most staff and all three headteachers,[57][58] the new Lincolnshire County Council voted to return the scheme for further consultation in January 1975, a move the Sleaford Standard called "politically motivated".

[57][60] The Education Act 1976 made it a duty on local authorities to "have regard to the general principle that ... education [they provide] is to be provided only in schools where the arrangements for the admission of pupils are not based ... on selection by reference to ability or aptitude", and it empowered the government to compel local authorities to prepare comprehensive schemes for their schools.

[77] The chair of the governors, Geoff Hotchkin, was quoted saying that this was because St George's College of Technology (the secondary modern school's successor) had converted to an academy, which meant that KSHS "cannot legally enter into any formal agreement with them.

[2][79] The following year, the Sleaford Target reported that the headteacher, Craig Booker, was proposing to introduce "an adjusted staffing structure" in anticipation of changes to the school's funding.

[92][n 4] Along with Carre's Grammar School and St George's Academy, KSHS is part of the Sleaford Joint Sixth Form,[95] which was founded in 1983.

[101] For entry into Year 7, prospective pupils sit the eleven-plus examination to assess aptitude; the test procedures are set by the school.

There is a statutory appeals procedure organised by the local authority and run by an independent panel whose decision is binding on all parties.

Prospective pupils in Years 8 to 11 must sit the nationally standardised cognitive ability test (CAT) for their age range (this includes verbal, non-verbal, quantitative and spatial elements).

[92] For Key Stage 3 pupils, the curriculum comprises art, computing, design and technology (incorporating food technology, textiles and graphics), drama, English, ethics and philosophy (EP), French, geography, German, history, mathematics, music, physical education (PE), science, and a personal development programme incorporating personal, social and health education (PSHE).

[109] In Key Stage 4 (Years 10 and 11), pupils study a core curriculum comprising English, mathematics, science, PE, EP and PSHE.

Students are required to take GCSEs in English language and literature, mathematics, science, either French or German, history and/or geography, EP, and two further subjects.

[111] The Joint Sixth Form allows pupils to choose from around 60 vocational or academic subjects including (as of 2024): A-Levels in biology; chemistry; computing; design engineering; drama; English language and/or literature; French; history; geography; German; fashion and textiles; law; mathematics; further mathematics; media studies; philosophy, ethics and religion; photography; physical education; physics; product design; psychology; sociology and Spanish.

[121] As of 2024, extra-curricular sports clubs include basketball, football, hockey, netball, tennis, badminton, volleyball, rounders, athletics, fitness, gymnastics and dance.

The second headmistress, F. M. Kirk, took girls on visits to the Lake and Peak Districts; outings to Paris and Stratford were smaller affairs, while a contingent travelled to the British Empire Exhibition at Wembley in 1924.

The company was active throughout the 1960s and 1970s, although Outram became divisional commander in 1969 and Misses Hudson and Broughton took over the school's guides, which were split into four patrols.

Between canted windows on either side, the central section projects forward with quoins and includes an arched doorway with pilasters.

[39] After the Second World War, the school's preparatory department closed and it ceased to take boarders, so parts of the house were gradually converted into classrooms and a library; the latter was funded by public donations, and opened in 1949.

[45] By the 1990s, the building had been converted into a Sixth Form study area and music classrooms, but part of it was deemed to be a fire hazard.

[27][n 7] These were supplemented in 1920 by wooden huts which provided an office for the headmistress, a biology room, an assembly hall, a cloakroom and three classrooms.

[39] To accommodate KSHS's growing roll, the playground and netball pitch were replaced by prefabricated concrete blocks containing classrooms, a canteen and a kitchen in 1946–47.

In the first phase, the Council erected a single-storey block of science classrooms and laboratories on the site of disused air-raid shelters.

[73] The new building was officially opened in June 1996 by the Lord-Lieutenant of Lincolnshire, Bridget Cracroft-Eley, with the local MP Douglas Hogg also in attendance.

[141][143] Another new block housing a library, three classrooms, a laboratory and office space was completed in September 2005 and officially opened in December 2006, when it was named after a former teacher, Jenny Cattermole.