The Bishop of Durham has voiced concerns that the Government is failing to give proper consideration to the concerns of religious parents around new relationships and sex education lessons.
Addressing the House of Lords, Bishop Paul Butler said that he was "deeply concerned" that relationships education was not being made optional for primary school children.
The change is being introduced by the Government in the biggest overhaul of relationships and sex education in schools in 20 years.
Under new legislation, parents will have the right to opt their children out of sex education at the primary school level, but not relationships education.
The changes, coming into effect in September 2020, will also limit the ability of parents to opt their children out of sex and relationships classes in secondary school, with head teachers reserving the right to enroll them in "exceptional circumstances" and students being able to decide for themselves after the age of 15.
The lessons have come under scrutiny because of concerns that they will undermine the rights of parents, particularly those of faith, to raise their children in line with their own beliefs.
Bishop Butler commended the legislation for placing the lessons within the "wider personal development of character, virtues and values".
"Conversations about relationships will be empowered by discussions of honesty, courage and humility," he said.
"Sex education is crucially paired in this framework with conversations about relationships: an incredibly important shift in how the curriculum is constructed."
However, he suggested that it was not appropriate to teach relationships lessons to primary school children.
"I am also glad that sex education will be optional in primary school. However, I am deeply concerned that the same cannot be said of relationships education," he said.
"Psychologists, ethicists and paediatricians often debate at what age and developmental stage it is appropriate to be exploring early concepts of relationality and sexuality.
"For example, girls continue to hit puberty earlier and earlier, while the average age of boys maturing remains more constant. How are schools to come to a conclusion about how and when they teach on such issues, and how will such decisions and resources then be adequately monitored?"
He added, "Development is not uniform, and parents should be able to determine what is appropriate for their children, especially during vulnerable ages. Why cannot parents' decision regarding what is appropriate for their children be respected?"
The bishop welcomed the emphasis on the special place of families in the new relationships curriculum but said that although the motives were honourable, it failed to respect the "diversity of parental concern".
He urged the Government to listen to the views of parents of faith.
"Our concern is that the views of others, especially respecting the beliefs of people of faith—and, indeed, some of no faith—about parental responsibilities and rights, are not simply brushed aside," he said.
"The lines between relationships and sex education are far more blurred than is recognised, so I ask that great care is taken to monitor that this does not lead to inappropriate sex education being offered at an early age in the name of relationships education."