Neil Foden, of Old Colwyn, was found guilty in May after a three-week trial at Mold Crown Court in north Wales.
The 66-year-old was previously headteacher at Ysgol Friars school in Bangor, Gwynedd.
He was found guilty of 19 charges in total – including 12 counts of sexual activity with a child and two counts of sexual activity with a child in a position of trust.
He was also convicted of one count each of causing or inciting a child to engage in sexual activity, attempting to arrange the commission of a child sex offence, sexual communication with a child, possession of indecent photographs of a child for show and sexual assault of a child under the age of 13.
The trial heard Foden had abused the four complainants over a period of four years.
The jury returned guilty verdicts and cleared Foden of one count of sexual activity with a child on Wednesday 15 May at Mold Crown Court.
Ceri Ellis-Jones, of the Crown Prosecution Service, said: “These crimes were shocking as Foden was a trusted and well-respected individual, who used that to his advantage. He abused his position of trust and targeted the most vulnerable females he was entrusted to safeguard.
“The victims are to be commended for their bravery in coming forward and giving evidence. Their support for this prosecution has been key to Foden being brought to justice.
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