Faced with declining rolls and competition from cheaper commercial schools, Carre's eventually added technical and artistic instruction to its Classical curriculum by affiliating with Kesteven County Council in 1895.

In 2024, the school received an "average" Progress 8 score; 67% of pupils achieved English and mathematics GCSEs at grade 5 or above, which was much higher than the national figure.

[6] An Office for Standards in Education, Children's Services and Skills (Ofsted) inspection in 2023 graded Carre's Grammar School as "good" in every category.

[10] Although the school received a bequest from a local gentleman, Robert Cammock, in 1631, which provided an additional income of £4 per annum, no more followed;[11] the English Civil War also disrupted funding: rents were not collected between 1644 and 1646.

[11] Carre's lagged behind other schools and its buildings fell into disrepair as the fixed endowment failed to keep up with inflation (despite the Gedney lands increasing in value to £180 by the early 19th century).

[12] In 1783, the foeffees (by then, often called trustees) spent £50 on improvements, but by 1794, the adjacent Carre's Hospital agreed that part of its building be pulled down to make way for a new schoolhouse.

When the charity commissioners inspected the school the following year, they recommended that an usher be appointed to teach "commercial education" to supplement the Classics.

[20] Although the trustees were reorganised in 1876, Britain's agriculture suffered from foreign competition in the 1880s, which contributed to a decline in the rolls; a subsequent reduction of fees in 1889 proved ineffective and only twelve boys were in attendance the following year.

[21] The Commissioner of Inquiries suggested that Kesteven County Council could support the teaching of art, modern languages and technical and scientific subjects through the Local Taxation Act 1890.

[24] From 1919, elementary school pupils sat the entrance exam each term and those who passed were allocated the places which remained after fee-paying students had enrolled.

[26] By 1955, the school had 330 pupils on roll[27] and the need for new accommodation was met in the 1950s and 1960s by a major building programme at the Northgate site; completed in 1966, this added dedicated classroom blocks, a canteen and hall.

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

[31] A new plan which envisaged Carre's becoming a sixth form college[31] was supported by parents in a vote (1,199 to 628), albeit with a 50% turnout; the County Council approved it but allowed governors a veto.

[69] Pupils applying at other times up to Year 11 must sit the nationally standardised cognitive ability test (CAT) for their age range (this includes verbal, non-verbal, quantitative and spatial elements).

Religious practice was a stipulation in the 1835 decree, which required pupils to pray at the start and end of each day and engage in daily readings of holy scriptures.

[74] In the mid-19th century, Carre's offered this classical education for free, but arithmetic, geometry and algebra were taught as extras at a rate of two guineas per term.

Students were enrolled from the age of eight, and were expected to be able to read, write, recite the Lord's Prayer, the Apostles' Creed and the Ten Commandments, and "be qualified to begin Latin grammar".

[76] In 1876, the curriculum was widened so that it comprised reading, writing, arithmetic, English, mathematics, history, geography, Latin, a foreign language, music, natural science and drawing, with Greek as an optional extra.

By the 1950s, a wide range were available: English language and literature, mathematics, French, German, Latin, Greek, art, history, geography, physics, chemistry and woodwork; biology was taught at Kesteven and Sleaford High School.

[72] The use of information technology is central to all teaching and is taught as a subject in Key Stage 3 and pupils may opt to take Computer Science as a GCSE.

The Robert Carre Trust and St. George's Academy operate the Sleaford Joint Sixth Form, which shares a common timetable between the three sites and allows for students to choose from a wide range of options at A-Level.

Most pupils took part in its activities in World War II, under the lead of the History teacher, Major W. H. T. Walker; this included athletics competitions, shooting practice and trips to camp sites.

Athletics were practised at the school as early as 1871 when a sports day was held; the 100 yards and half a mile races, hurdles, the pole jump and throwing the cricket ball were activities in which forms competed.

[91] A cycling club was formed in the 1940s[92] and badminton was informally organised by pupils by the 1950s; between 1957 and 1960, a portion of land was converted into tennis courts for the school and rugby was introduced in the 1966–67 academic year.

"[95] In 2021-22, the school took part in the National Rotary Youth Speaks Competition which involved a team of 3 creating and debating a subject of their choice.

In 1834, the Chancery Court agreed to fund the rebuilding of the school according to plans by the Sleaford architect and builder Charles Kirk, who constructed it at a cost £1,168 15s.

[48] A building programme costing £835,000 provided the school with food technology facilities and a two-storey Fitness Suite, which were opened in March 2011.

1959)[151] and Captain George Baldwin, CBE, DSO (1921–2005), who served in World War II and as Director of Naval Air Warfare in the mid-1960s.

[152] The lawyer and controversialist John Austin (1613–1669) was educated at Carre's, along with the Royalist poet Thomas Shipman (1632–1680) and the non-conformist clergyman Andrew Kippis, FRS (1725–1795).

[153] Science is represented by the chemist Kenneth Wade, FRS (1932–2014), a professor at Durham University,[154] and the forensic pathologist Iain West (1944–2001).