Piotr Zaloba pleaded guilty last month to charges of sexual interference, luring a child and publishing child pornography.
He originally faced two counts of sexual assault, but those charges were not part of the plea agreement.
According to an agreed statement of facts read in court Monday, Zaloba met the two students through his position as a temporary-contract teacher at St. Basil Catholic School in north Edmonton.
St. Basil is a K-9 school with 400 students, and offers a Polish bilingual program and an all-girls leadership academy.
Zaloba was charged after the 15-year-old girl came forward in March 2013.
He faced more charges the following month, when the 13 year old went to police.
Zaloba's relationship with the 15 year old included more than 5,000 texts and Skype sessions that ranged from graphic photographs to masturbation videos, Crown prosecutor Diane Hollinshead said at the sentencing hearing.
The relationship later became physical, with sexual liaisons at the school, she said.
Hollinshead said Zaloba sent more than 10,000 texts to the 13 year old, pressuring her to have sex with him, telling her she was beautiful and he wanted to marry her.
When she resisted, Zaloba messages included, "You've entered the wrong crazy man's playground," and, "This is a last ditch effort before I walk into traffic."
He also asked her if there were other girls who found him attractive.
Zaloba eventually kissed the 13 year old, but she told him "it just doesn't feel right."
Zaloba's sentencing will continue in October, when victim impact statements are expected to be submitted.