When was the school founded which makes up Sleaford Joint Sixth Form with St George's Academy ? 
Sleaford Joint Sixth Form: Sleaford Joint Sixth Form is a partnership in Sleaford, England, between Carre's Grammar School and St George's Academy. Carre's Grammar School:  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.
1 September 1604