A former teacher from Heanor admitted 21 sex charges involving school girls and adults.
Russell Singleton admitted abusing his position of trust while working at Alfreton Grange Arts College, formerly known as Mortimer Wilson Secondary School.
He pleaded guilty to seven charges of sexual activity when he was in a position of trust; nine of taking indecent photographs; two of making indecent photographs and three charges of voyeurism.
Singleton, 56, of Lawn Close, admitted the charges at Nottingham Crown Court on Tuesday morning and has been bailed. He is due to return to be sentenced on April 22.
Detective Sergeant Toby Fawcett-Greaves from the forces Public Protection Unit, said: “Singleton acted alone in what was a sophisticated pre-planned scheme to capture indecent images of adults and children for his own sexual gratification.
“We welcome the guilty plea to all offences, which has prevented his victims having to relive the ordeal in court.
“This has been a long and determined investigation and it is a true testament to the courage of the victims who came forward.
“We worked closely with the Crown Prosecution Service to bring this man to court and we hope his victims will now be able to put this behind them.”