Church of England congregations with the largest under-16 attendance are conservative on sexuality, a study by Christian Concern has found.
The study examined 33 churches and found that 20 of them (61%) supported the Church's historic view on marriage as a lifelong union between a man and a woman.
None of the churches or their leadership publicly expressed support for changing the Church's doctrine on marriage.
Christian Concern's chief executive Andrea Williams, who served on the Church of England's General Synod for 10 years commented, "The complete absence of churches which publicly support for revisionist beliefs on marriage shows that it is entirely possible for churches in the 21st century to reach and retain young people while teaching historic, orthodox beliefs on sexuality.
"Young people are bombarded by messages that sow confusion about who they are. They have seen the damage caused by broken marriages, pornography and sexual liberation and they want something different. Faithful, loving Christian churches and youth groups which don't preach LGBT ideology are places of comfort and healing for them.
"God has clearly spoken on sexuality through his word: sex is reserved for one man, one woman marriage. Nevertheless, one of the arguments of those who want to change doctrine is that it is necessary to reach the next generation. This research shows the complete lack of evidence that any change is required."
The churches in the study appeared on a list provided to General Synod in 2019 of congregations with over 100 under-16s attending from 2015 to 2017 – the most recent available public data.
The study was based on the churches' websites and social media presence, and included online sermons, profiles and public statements by senior church leaders.
The analysis was carried out in response to plans in the Church of England to permit services of blessing for same-sex couples.
The controversial proposals will be debated at the Church's General Synod in London next week.
The analysis is also a response to the Bishop of Oxford's suggestion that changing its doctrine would benefit the Church in its outreach to younger generations.
In his paper, Together in Love and Faith, published in December, Bishop Stephen Croft wrote: "In paying attention to our prevailing culture, particularly as expressed by the under forties, I am aware of their sense of this manifest unfairness, and of anger and alienation among a whole generation.
"If the Church believes this clear injustice, the argument goes, then what does this say about the rest of the beliefs of the Church? Is this an organisation that is to be taken seriously at all as a moral and ethical force in the 21st century?"
Ms Williams said that the proposals to bless same-sex couples, if approved, could lead to the Church's decline.
"Blessings for same-sex partnerships would be wrong in principle, but it could well hasten the Church's decline in practice," she said.
"Faithful churches and ministers with vibrant and growing congregations might reconsider their relationship to the Church of England. And those preaching the same message as the world, with no sin, no need for repentance and therefore no need for Christ will find themselves with no congregation to pay the bills.
"God does not bless sin, and he does not bless those who bless sin."