Reisz was a founder member of the Free Cinema documentary film movement. His first short film Momma Don't Allow (1955), co-directed with Tony Richardson, was included in the first Free Cinema program shown at the National Film Theatre in February 1956. His film We Are the Lambeth Boys (1959) was a naturalistic depiction of the members of a South London boys' club, which was unusual in showing the leisure life of working-class teenagers as it was, with skiffle music and cigarettes, cricket, drawing and discussion groups. The film represented Britain at the Venice Film Festival. The BBC made two follow-up films about the same people and youth club, broadcast in 1985.