A man who had many roles in his 36 years with a Calgary young people's performance group has admitted to eight sex-related charges.

Philip Heerema's trial on 20 charges was already into its third week when he pleaded guilty on Tuesday.

Heerema, 55, resigned in 2014 from The Young Canadians School of Performing Arts in Calgary when police began investigating several complaints.

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The alleged victims were male students between 15 and 18 years old who were at the school between 1992 and 2013.

The trial had heard from several men who said Heerema convinced them to send him explicit photos.

One man said he felt trapped after exchanging naked photos with Heerema.

"I couldn't talk to anyone about what was happening because then Phil would presumably get in trouble and that wouldn't be good for anyone," the man testified.

He eventually told a family member what had happened and went to police.

The school works with students between 11 and 18 years old in dance, voice and performance. Training culminates in grandstand shows during the Calgary Stampede every July.

Heerema started out as a performer with The Young Canadians and took on a number of jobs that included costuming, props, sets and lighting. He was business administrator and production services co-ordinator when he resigned.