Anthony Paul Leake, 65, worked as a teacher in Fleetwood in the 1970s and, during a three-year period between 1972 and 1975, he identified vulnerable children and invited them to stay with him in a caravan in Dent, Cumbria.
He groomed four victims and enticed them to engage in acts of gross indecency which he would then record on to film.
And he continued his offending in the 1980s while living in Cromer, Norfolk, where he made indecent images of children and sexually assaulted a young girl.
In the 1990s Leake’s behaviour continued, where he again incited a young boy to engage in an act of gross indecency.
When arrested, Leake was found to be in possession of the indecent images and film footage he had made.
Most of his victims were aged between 10 and 13, police said.
Last week he was sentenced to nine-and-a-half years in prison at Carlisle Crown Court for a total of 26 historical child sex offences.
Det Con Damian West, who led the investigation for police in Cumbria, said: “All of the victims have shown tremendous courage in coming forward and speaking about what happened to them.
“Leake was a predator who identified children who were vulnerable, befriended them, and then manipulated them into doing what he wanted. He is now where he belongs – in prison.
“The sentence given should give his victims some sense of justice and hopefully some form of closure.
“This case highlights how dedicated Cumbria Police are in investigating child abuse, however long ago it happened, and we encourage anyone who has been a victim to come forward.”