Accelerated Christian Education, or ACE, is infamous for its controversial independent learning style and for teaching in line with fundamental Christianity – the curriculum hit the headlines in 2012 when it was discovered that some resources used the existence of the Loch Ness Monster to disprove Darwin's theory of evolution.

It isn't known exactly how many ACE schools are currently operating in the UK, but it is thought to be between 25 and 50. Critics lambast the curriculum as right-wing, conservative indoctrination, while its supporters claim it merely nurtures a Christian understanding of the world within a religious framework.

Jonny Scaramanga, who attended Victory Christian School in Bath for three and a half years, however, is determined to prove that ACE "robs children of educational and intellectual opportunities".

Now in his late 20s, Scaramanga was bought up as an evangelical Christian and started his secondary education at Victory, but left when he reached Year 10 after a period of depression and having what he describes as a "meltdown". He became disillusioned with some of the school's teachings and eventually renounced Christianity, choosing instead to identify himself as an atheist.

Though he now campaigns against ACE, Scaramanga told Christian Today that he initially enjoyed his time there.

"To begin with I loved it. During the first four terms at least I was very happy indeed – I felt that I was where God wanted me to be, and I felt very privileged to be in an environment that I loved," he said.

"There were always things that concerned me from the beginning though – paddling [the act of striking a 'disobedient' pupil with a wooden paddle] was prominently used as a punishment at Victory and I was really afraid of it. It seemed to be used frequently for offences that even at the time didn't feel justified, and I lived in fear. There were other physical punishments too that I was really afraid of, but I generally liked the curriculum and I'd never been sociable so working alone was great and I loved that I could hurry ahead with my work."

ACE students follow a curriculum based on 'PACEs' – booklets which facilitate independent study. Pupils study at individual desks, and are encouraged to set their own goals; there is little interaction with other pupils or teachers. Scaramanga says the work was "incredibly easy", but didn't allow any room for questioning or developing beliefs that contradicted the fundamentalist views it supported.

"There is nothing in the ACE curriculum which fosters the development of critical thinking skills. The environment of the school is not conducive to questioning certain beliefs, and people in favour of the school say 'Isn't it so wonderful that there's no peer pressure', but there was peer pressure, it was just in a different direction," he says.

"Everyone expressing unity of belief makes it difficult for you to think differently."

One of the main sources of contention regarding the ACE curriculum is its focus on creationism as opposed to evolution – a belief pressed so strongly upon students that Scaramanga says he didn't even question it until he was 23, long after he had left the school.

"Everything ACE taught about evolution was misleading – which is true even if Creationism is true. Evolution is not according to scientists as it is depicted in the PACEs, and it's doing no one any favours to misrepresent what scientists think.

"But I'm more concerned about teaching that says it's bad to be friends with people who aren't Christians, or even the right kind of Christians – and there's a very restricted definition of who is a Christian – and their idea of purity culture and modesty culture; policing what women wear and saying women should submit. ACE supporters would disagree, but I would say the PACEs depict women as second class citizens."

Despite his strong feelings about ACE and his time at Victory, however, Scaramanga is keen to open up dialogue about fundamentalist Christian education and hear from those who have had more positive experiences than himself. He has even asked those who support ACE to contribute to his blog, 'Leaving Fundamentalism'.

"A lot of it is for my own morbid curiosity. I don't understand how anyone can see any good in it – it makes me think is there something I haven't considered?" he explained.

"When I was in ACE I was the most rigid and closed minded kind of fundamentalist – I was so certain that I was right that I didn't think I needed to listen to anybody else because I knew what God thought.

"I'm determined not to be like that again – I'm always hunting for another point of view I haven't considered. It's also important not to create a straw man of what it is to be a supporter of ACE – I want to understand what that's like, and there are some legitimate concerns that people have about children from conservative Christian backgrounds being bullied in mainstream schools, and we need to listen to that."

Scaramanga was featured on Newsnight last week, during an episode in which Jeremy Paxman – in one of his final shows as presenter – interviewed John Lewis, director of Christian Education Europe which promotes and supports ACE. Lewis claimed that he and his siblings, all of whom were taught through ACE and have gone on to excel academically, received an excellent education.

In addition, Jeremy Vine interviewed Scaramanga and Giles Boulton, who also went to Victory School and now works at Maranatha Christian School near Swindon. Like Lewis, Boulton defended ACE, arguing that it can be used alongside other curriculums for a well-rounded education.

Scaramanga, however, refutes their claims. "I don't believe they had a great education. I've never met John Lewis, but I know Giles very well and he's quite brilliant – a number of children were at Victory, they were the kind who would have thrived anywhere. Every year there are children at failing secondary schools who make it into top universities and that doesn't show the school's rating is wrong, but it's evidence of how resilient children can be, and that they're able to thrive in circumstances that aren't ideal," he said.

"There are some children who succeeded in ACE, undoubtedly, and it's certainly true that the style of individual learning suits some children, but I think there's no question that the ACE curriculum is not ideal – it goes against all we know about how children learn and how knowledge works.

"So they [Lewis and Boulton] can't have had an ideal education, but I can believe that they thrived in spite of that. But then that doesn't mean we should ignore cases of children who had the reverse experience – who were damaged by ACE. It may be that it's only a small minority who were damaged or let down by the curriculum and struggled, but I'm a teacher and if I found any of my pupils were struggling, I would want to hear about it and understand and know what I could do to change it. It saddens me that my old teachers at Victory, ACE and ACE Europe aren't interesting in learning."

As for faith-based education in general, Scaramanga isn't entirely against it – but he says children must always be freedom of choice, and it's important to encourage diversity within the education system.

"I don't think it's right to say to children: 'This is what you should believe' when it's a matter of faith and a matter of conscience. It's dishonest to say 'We know this is true' when we don't know that it is," he argued.

"I don't think it's impossible to have a school with a faith ethic that provides a good education, but it doesn't do us any favours to have children from families with different beliefs going to different schools. Some of my most beneficial learning experiences have been when I've been with people of different religious views and no religious views."

Interestingly, the majority of ACE schools have received 'Good' or 'Outstanding' ratings from independent inspection authority Ofsted, though Scaramanga suggests he is sceptical about how thorough these inspections could have been. "It seems possible that Ofsted has been making sure that pupils are making progress, rather than looking at the content of the curriculum," he noted.

"I think it doesn't make sense to accredit qualifications where it's possible to pass tests without understanding the work. Some children may have undertaken the ACE curriculum and gone onto excel, but some may not. We don't know from test results, so we shouldn't validate it.

"If Ofsted looked at it properly, parents would be able to make a more informed choice. It should be made clear there are certain aspects of the curriculum that are controversial – the PACEs teach that God is politically right-wing, so the further left you go, the further away from God you are. Many Christians have a problem with that, and yet no one said anything to me when I was learning that – no one said: 'You don't have to believe that' or 'It's controversial' – I swallowed it whole."

Despite having a strong evangelical faith when he was young, even being featured on a promotional video for Victory in which he discusses speaking in tongues and how "wonderful" God is, Scaramanga now says he feels entirely removed from that time in his life.

"I've had even more powerful experiences since," he says of his move away from Christianity. "I've been a musician and I've had similarly ecstatic moments when I've been improvising and playing with other musicians. I think it's best explained in terms of human psychology – you could possibly say it was God, but certainly not exclusively the Holy Ghost that I believed in then.

"Now I wouldn't attribute it to God at all, and it [speaking in tongues] is definitely not evidence that that is truth – people are having equally powerful experiences even though they believe the exact opposite of what I did.

"When I left church secular music made me feel euphoric, which I'd always attributed to anointing before, but the how come with secular music it was better?" he asked.

Whatever the lasting effects, Scaramanga is clear that his Christian past is behind him: "There are times when I struggle to understand how I ever believed."