In 1700 a Trust was established by Sir Walter St John for the continued provision of a school to provide free education for twenty poor boys from Battersea. By 1750 the school had nearly 90 pupils, and was the only school of significance in Battersea until a school was established there by the Society for the Propagation of Christian Knowledge in 1799. The two schools were run as one for part of the first half of the 19th century, and separated out again in 1853. In the 1870s an upper school for 250 fee-paying scholars was proposed as an addition to the elementary school. The original twenty free places were to be safeguarded at the latter.
The Upper School, shortly renamed Battersea Grammar School, opened on 12th April 1875 on St John's Hill, Battersea. The second headmaster, William Henry Brindley who originally joined the school as an assistant master, was appointed in 1881, to what was then a school of 48 pupils. In 1936 the school moved to purpose built premises in Abbotswood Road, Streatham. During the Second World War pupils were evacuated first to Worthing then to Hertford. As a result of lack of funds, the school became a controlled school in the late 1940s. It closed in 1977, and staff and pupils were amalgamated with those of the Rosa Bassett Grammar School in the new Furzedown Secondary School. In 1993 the Abbotswood Road site was taken over by Streatham Hill and Clapham High School.
Headmasters of Battersea Grammar School were Rev Edmund A Richardson, 1875-1881, William Bindley, 1881-1918, Henry Ellis, 1918-1945, Walter Langford, 1945-1965, James Cowan, 1965-1972, and John Phillips, 1973-1977.
The Old Grammarians' Association was founded on 16 July 1902, although Old Grammarians had held a variety of recreational and social functions prior to this, and it continued to provide social and recreational activities for old boys of Battersea Grammar School throughout the 20th century. It is still in existence at the time of writing, seee www.oldgrammarians.co.uk (correct at time of writing, January 2011).
The Sir Walter St John's Schools Trust was from 1875-1949 the governing body of both schools. After 1949 it existed largely to handle the funds of the Trust, to nominate a proportion of governors and help the schools by making grants.
Sir Walter St John's School continued in existence until 1986. At the time of writing the site houses the Thomas' Day School.