Some parents of children at a Vacaville, Calif., elementary school have complained that they were not notified before a teacher’s gender reassignment surgery.

The parents told the Travis Unified School District that they believe they had a right to know before the school year began that a Foxboro Elementary School music teacher, whose name was not released, underwent gender reassignment surgery during the summer break and now uses the honorific “Mister,” KCRA-TV, Sacramento, Calif., reported Thursday.

The school board said such disclosure would violate privacy rules under the Health Insurance Portability and Accountability Act.

Twenty-three students from 15 different families have been transferred out of the music class since the beginning of the school year.