CHICAGO (CBS) — A former teacher at a northwest suburban Christian school has pleaded guilty to fondling himself during class.

Paul LaDuke, 75, was fired from Schaumburg Christian School five months ago, where he admits he was fondling himself during an algebra class.

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He says it wasn’t the first time.

LaDuke’s attorney claims his client has a diagnosed brain condition that makes him impulsive.

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LaDuke was arrested after a student at the Schaumburg Christian School told another teacher that LaDuke unzipped his pants while sitting behind a podium, then masturbated while his students were in the classroom.

Several students later interviewed by police offered similar accounts, authorities have said.

Cook County Assistant State’s Attorney Dave Weiner told the judge in November that prosecutors have a handwritten note from LaDuke, in which he admited to fantasizing about female students while masturbating in class for the past 10 years.

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He’s been sentenced to 30 months probation and must register as a sex offender.