Penistone Grammar School (PGS) is a co-educational secondary school and sixth form located in Penistone, South Yorkshire, England. Founded in 1392, it is the 45th oldest extant school in England with its most notable alumnus being Nicholas Saunderson, the probable inventor of Bayes theorem, in the 18th century. The school has undergone many expansions, requiring the erection of several buildings, and now houses over 1,700 pupils from age 11 to 18. PGS' Ofsted overall rating is grade 2 ('Good'), following an inspection in November 2017.