Ben Breakwell, 40, of Monkgate, York, abused his position at a west London school to engage girls in sexual activity between 2014 and 2017.
Breakwell kissed a third victim, aged 16, in a lesson and possessed indecent images of a fourth, Isleworth Crown Court heard.
He remains in custody and will be sentenced on 14 October.
Breakwell's crimes came to light after the third victim told friends and then her mother. The mother confronted Breakwell who denied deliberately kissing her.
The victim later told police that she felt guilty about what had happened as she had bought him a box of sweets as a thank you present and thought that this may have encouraged him.
In September 2017, the friends of one of the victims approached a member of school staff with suspicions about an inappropriate relationship involving Breakwell.
The school immediately suspended him and police launched an investigation before arresting Breakwell in November 2017.
He was charged in February 2020 and convicted on Monday of 22 counts of sexual activity with a child, three counts of causing or inciting a child to engage in sexual activity, four counts of sexual activity with a child by a person in a position of trust, one count of sexual assault, and two counts of taking indecent photographs of a child.
Det Con Ben Lawrence-Smith urged other potential victims to come forward.
He said: "My thoughts are with the young girls who were betrayed by Breakwell. They have all been incredibly brave and it is their courage in speaking out that has brought him to justice.
"Breakwell deceived and abused these girls and then sought to evade any responsibility for his actions. They were manipulated to the point where some felt it was they who were doing wrong. The fact Breakwell was a teacher only compounds this gross betrayal of trust.
"It is clear that Breakwell was a sexual predator who carefully manipulated these young girls in order to exploit them.
"His victims were very young and he led them to believe they were in love with him, knowing that if they cared for him they were less likely to alert anyone to his crimes."