 Former pupils are known as " Old Grammarians " . The school has a number of notable alumni . The earliest recorded alumnus is Thomas Herring ( 1693 – 1757 ) , who was Archbishop of Canterbury between 1747 and 1757 . Perhaps the most famous alumnus is the abolitionist , Thomas Clarkson ( 1760 – 1846 ) , whose father , John , was headmaster at the school . His essay on slavery and subsequent campaigning led to the foundation of the Committee for the Abolition of the Slave Trade and the passage of the Slave Trade Act of 1807 , which ended British trade in slaves . Thomas Clarkson 's younger brother John Clarkson ( 1764 – 1828 ) also attended the school . He subscribed to his brother 's abolitionist cause , and became the first governor of the free Sierra Leone colony , founding the country 's capital city , Freetown . 
