Question: When was the school founded which makes up Sleaford Joint Sixth Form with St George's Academy ? 

Context articles: Carre's Grammar School
Blackfen School for Girls
St George's Academy
St Bede's Catholic School and Sixth Form College
Kirk Hallam Community Academy
St George's School, Birmingham
Sleaford Joint Sixth Form
Claydon High School
Ursuline High School, Wimbledon
St George's Church of England Foundation School

Carre's Grammar School is a selective secondary school for boys in Sleaford, a market town in Lincolnshire, England.
 Founded on 1 September 1604 by an indenture of Robert Carre, the school was funded by rents from farmland and run by a group of trustees.
 The indenture restricted the endowment to £20 without accounting for inflation, causing the school to decline during the 18th century and effectively close in 1816.
 Revived by a decree from the Court of Chancery in 1830, new buildings were constructed at its present site and the school re-opened in 1835.
 Faced with competition from cheaper commercial schools and declining rolls, Carre's eventually added technical and artistic instruction to its Classical curriculum by affiliating with Kesteven County Council in 1895.
 Following the Education Act 1944, school fees were abolished and Carre's became Voluntary Aided.
 New buildings were completed in 1966 to house the rising number of students.
 After plans for comprehensive education in Sleaford came to nothing in the 1970s and 1980s, Carre's converted to grant-maintained status in 1990.
 Foundation status followed and the school became an Academy in 2011; a multi-Academy trust with Kesteven and Sleaford High School was formed in 2015.
Blackfen School for Girls is a girls' secondary school and sixth form with academy status, located in Blackfen in the London Borough of Bexley, England.
 Although it is a girls school, the sixth form over the past few years has become mixed.
 This is due to the partner school Hurstmere Foundation School having no sixth form, so many pupils from Hurstmere join the sixth form in Blackfen school.
 The headmaster is currently Matthew Brown, having previously been Louise Sharples.
 The school gained specialist status in Maths and Computing in 2004.
 Compared with many other secondary schools in the area, it is one of the highest achieving in terms of GCSE and A-level results.
 The percentage of students gaining five or more A* to C, including English and Mathematics was almost 64% in 2011, an 8% increase on the previous year.
 Five or more A* to C grades were gained by 82% of students and almost 25% of students gained three A* or A grades.
St George's Academy is a co-educational comprehensive secondary school based in the English market town of Sleaford in Lincolnshire, with a satellite school at nearby Ruskington.
 Its origins date to 1908, when Sleaford Council School opened at Church Lane to meet the growing demand for elementary education in the town.
 After the Education Act 1944, the senior department became a secondary modern.
 A second school building was constructed at Westholme in the 1950s and expanded in 1983, allowing the Church Lane site to close; to mark the occasion, it was renamed St George's School.
 After it became grant-maintained, the school became a comprehensive, received a Technology specialism, became a Technology College in 1994 and later converted to Foundation status.
 Coteland's School in Ruskington federated with St George's in 2007; they merged to form the Academy in 2010.
St Bede's Catholic School and Sixth Form College is a coeducational secondary school and sixth form with academy status, located in Lanchester, County Durham, England.
 It has a main block, a language block, a technology/music block, the sixth form block, two fields, tennis/basketball court and an astroturf.
 On 1 June 2012 the school became an academy, giving it independence from the local authority.
Kirk Hallam Community Academy is an academy school in Derbyshire, UK.
 The school has satisfactory Ofsted results.
 The school a sixth form that was visited by Gordon Brown in 2009.
 The sixth form, named "The Lakeside Centre", is part of the Ilkeston Sixth Form Partnership.
 The Principal is Mr. M. D. Ebbage, though Mr Cowley in majority runs the Sixth Form.
 Previously Mr E Hamer was the Head Teacher.
 In September 2014 the school changed its name to Kirk Hallam Community Academy.
St George’s School is a non-selective independent day school in Edgbaston, Birmingham, England for girls and boys aged 11 to 18.
 It is located near St George's Church and consists of a lower school, an upper school and a sixth form.
Sleaford Joint Sixth Form is a partnership in Sleaford, England, between Carre's Grammar School and St George's Academy.
 It has Mathematics, Science and Computing specialism.
Claydon High School is a relatively small mixed secondary school in Claydon, Suffolk, England.
 The school is on the outskirts of Ipswich, just off the A14 and close to the A12 southbound.
 It shared a joint sixth form with Thurleston High School until July 2010, when their sixth form closed.
The Ursuline High School, Wimbledon (“the Ursuline”) is a government-maintained, voluntary-aided, Roman Catholic Secondary School for girls aged 11 to 19.
 The school is based at Crescent Road and the Downs, Wimbledon, London.
 It was founded in 1892 by the Ursulines.
 It is affiliated with The Ursuline Preparatory School, its previous feeder preparatory school.
 As well as Wimbledon College, the high schools brother school, who have worked in partnership since 1986 and share joint Sixth Form.
 The school specialises in Business & Enterprise and Modern Foreign Languages and it was previously designated a Gifted & Talented Lead School.
St George's C of E Foundation School, often abbreviated to St George's, is an all-through school in Broadstairs, Kent, catering for students for 4 to 19 years.
 The official School as it currently stands was formed in the mid 1970s by joining the two old schools of St George's Boys School and St George's Girls C of E School together into one building and formed the current St George's community.
 The student executive team is set up using 10 year 11 students.
 Along with the Head Boy and Girl they help run and support events such as the choir service and celebration evenings.