Prosecutors are asking Ontario's highest court to overturn the acquittal of a former violin teacher who measured his teenage students' bare breasts while fitting them for shoulder rests.

The Crown is appealing a ruling that found the 73-year-old not guilty on dozens of charges related to the sexual violation of more than 20 students in the 1970s and 80s, saying the trial judge made several errors.

The Chatham, Ont. man, was acquitted last year after a judge found the now-retired music teacher did not act with a sexual purpose but rather because he believed it was necessary to properly equip the students.

The appeal is set to be heard Tuesday and prosecutors are asking the court to convict the accused on some of the charges or order a new trial on all of them.

Court documents filed ahead of the hearing say the complainants, who are now adults, testified they were asked to remove their shirt and bra on the left side so that he could measure them from collarbone to nipple.

They testified he touched their breast during this process and often would then have them play with their left breast exposed. Four complainants also alleged he took a plastic mould of their left breast.