(CNN) -- Gay and lesbian groups are attacking a decision by the archdiocese of Denver, Colorado, not to re-enroll a child in a Catholic school in Boulder, Colorado, next year because the child's parents are lesbians.
The issue centers on the Sacred Heart of Jesus School, where the pre-schooler is currently enrolled.
"The Archdiocese of Denver has acted very unjustly in singling out this child for exclusion," said DignityUSA Executive Director Marianne Duddy-Burke in a written statement Monday. "Until every student's parents are tested on Catholic teaching, this action by Catholic officials cannot be understood as anything other than discrimination on the back of a child. At a tender age, this child has learned that Catholic officials are willing to inflict pain on children and families."
The decision was made public last week.
"These actions by the Denver Archdiocese harm the student by taking the child away from friends, teachers and community," said Jarrett Barrios, president of the Gay & Lesbian Alliance Against Defamation. "It's deeply troubling to see any school remove a child from their educational program simply as the means of rejecting that child's parents."
But the archdiocese defended its decision.
"Parents living in open discord with Catholic teaching in areas of faith and morals unfortunately choose by their actions to disqualify their children from enrollment," it said in a statement posted on its Web site. "To allow children in these circumstances to continue in our school would be a cause of confusion for the student in that what they are being taught in school conflicts with what they experience in the home.
"We communicated the policy to the couple at Sacred Heart of Jesus Catholic School as soon as we realized the situation. We discussed the reasons with them and have sought to respond in a way that does not abruptly displace the student but at the same time respects the integrity of the Catholic school's philosophy."
In a posting of his sermon, the Rev. Bill Breslin, pastor of Sacred Heart of Jesus Church, supported the move.
"The issue is not about our not accepting 'sinners,' " he said. "It is not about punishing the child for the sins of his or her parents. It is simply that the lesbian couple is saying that their relationship is a good one that should be accepted by everyone; and the Church cannot agree to that."
About 30 opponents of the move -- "mostly hetero allies of the gay community" -- protested Sunday outside the church during Mass, said Dave Ensign, board president of Boulder Pride, a lesbian, gay, bisexual and transgender community center and services organization.
Ensign handed out flyers to the protesters and then joined the parishioners as they listened to the sermon defending the church's move. "I was disappointed, but it was pretty much what I was expecting to hear," he said.
He added that the larger community's reaction has been positive, saying, "When people hear about this, they speak up, and I think that says a lot about our community."
The child has not been identified publicly. No one at the archdiocese or at the school immediately returned calls Monday seeking comment.