Holmes was a successful schoolmaster, teaching classical and modern languages, oratory, and drama, and he reversed the school's decline under his predecessors.
He soon found he needed to improve on the teaching materials he had inherited and decided to expand his career by writing and publishing school textbooks.
At Gresham's he pioneered the teaching of modern languages, especially French, as well as geography, and astronomy.
According to an advertisement in Holmes's Latin Grammar of 1732, Gresham's School under him taught Arithmetic in all its parts, Bookkeeping by Double Entry... the Use of Globes and writing in all the hands used in Great Britain.Holmes's headship was applauded by the Fishmongers' Company.
Critical pamphlets were aimed at his Greek Grammar, to which Holmes replied in letters to the press, using the pen-name Patroclus.