A reform school was a penal institution, generally for teenagers mainly operating between 1830 and 1900. In the United Kingdom and its colonies reformatories commonly called reform schools were set up from 1854 onwards for youngsters who were convicted of a crime as an alternative to an adult prison. In parallel, "Industrial schools" were set up for vagrants and children needing protection. Both were 'certified' by the government from 1857, and in 1932 the systems merged and both were 'approved' and became approved schools.

Both in the United Kingdom and United States, they came out of social concerns about cities, poverty, immigration, and vagrancy following industrialization, as well as from a shift in society's attitude from retribution, punishing the miscreant to reforming.

They were distinct from borstals (1902-1982 UK), which were enclosed juvenile prisons.