BOSTON — The parents of a slain Danvers math teacher say they feel a sense of “betrayal and anguish” over a court ruling that it is unconstitutional to sentence juveniles to prison without possibility of parole.

Colleen Ritzer, 24, was found slain behind the school in October, and her former student Philip Chism, 14, has been charged.

The Massachusetts Supreme Judicial Court ruled last month that juveniles convicted of first-degree murder should have the chance of parole in part because their brains are not fully developed.

The Ritzers in their statement Friday said “paroling such violent offenders would be more cruel and unusual punishment to victims’ families.”