Matthew Smith, from East Dulwich, south-east London, began work at Thomas’s Preparatory School in Battersea last September after teaching in Nepal.
The 34-year-old was arrested by the National Crime Agency after investigators discovered he was sharing abuse material on the dark web.
At the time of his arrest, he was online speaking to a teenage boy living in India, asking him to send sexual images of a younger child, in return for money.
Southwark Crown Court was told Smith had dark-web sites and forums open on his computer which were dedicated to child sexual abuse.
He was charged the following day with five offences, including causing the sexual exploitation of a child under 13, and remanded in custody.
Chat logs and financial transactions showed the ex-teacher had paid that same teenager, and another, also based in India, £65,398 to abuse children over a five-year period.
The court heard he would instruct the young men to perform sexual acts on boys and would send them images and videos as examples of ones he would like to receive in return.
Smith also gave one boy advice on how to befriend children and build their trust to abuse them.
More than 120,000 indecent images of children were found saved on his laptop, SD card and his phone.
Helen Dore, senior officer of the National Crime Agency, said: ‘Matthew Smith was a high risk individual and we moved quickly to locate, arrest and remand him so he could no longer pose a threat to children.
‘Ultimately, we were able to prove that he was a prolific offender who manipulated young men to sexually abuse children on his behalf, giving them detailed instructions and financial reward.
‘While conducting his offending, Smith worked at a school in Nepal, then became a deputy head teacher and head of pastoral care in the UK, so his offending is a deep betrayal of the trust placed in him.’
Smith pleaded guilty to the initial offences in November 2022, and to additional charges on Tuesday.
Last month, he was charged with a further 17 counts, including encouraging the rape of a child under 13, causing a child under 13 to engage in sexual activity, and arranging the sexual abuse of a child.
He is due to be sentenced on August 4, 2023.
Claire Brinton, specialist prosecutor in the CPS’ Organised Child Sexual Abuse Unit, said: ‘Smith’s crimes are particularly disturbing given his role as a primary school teacher entrusted with the responsibility of caring for and safeguarding children.
‘Thousands of images and videos were recovered from his devices which showed an appalling catalogue of sexual abuse being perpetrated on children.
‘Smith offered individuals payments for indecent images to gratify his own sexual desires, which resulted in the horrifying abuse of young children in India.’
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