Ex classmates of Shamima Begum said they felt "pressured" to join her and claimed she wore an ISIS badge on her blazer to recruit students.
Former pupils at Bethnal Green Academy spoke out for the first time since their ex classmate left to join ISIS in 2015.
Speaking to MyLondon, one pupil who remains anonymous said: "They were really pressuring about it, they were like 'you know, if you don't go to Islam you are going to hell and you are going to die.
“I never heard anything about ISIS violence. What you got pitched was a sunny, beautiful, idyllic place."
The pupil said Shamima Begum and Amira Abase would wear matching pins on the side of their blazers. It was a black flag with white Arabic writing on it.
He said the girls transformed in a matter of months and became "obsessed" with trying to rope people in.
Students were also left trying to piece together what had happened to another school girl, unrelated to Shamma, who went missing around Christmas 2014.
It later transpired she had also travelled to join ISIS in Syria.
Once the trio left, a strict regime was installed to prevent any other students leaving and everyone had to register with a police officer in the morning.
They were also banned from speaking about their classmates who's disappeared.
He said “If you utter one word about it you were in detention.
“It felt like you were in an authoritarian regime where you're controlled and can't say certain stuff.”
Despite what happened, he said he would give Shamima a hug if he saw her again.
He said: "If I saw her again the first thing I would do is give her a hug. I always believe in second chances, people make mistakes. I personally forgive her for trying to rope us into it.'
“She felt helpless, I'm pretty sure she still feels helpless, there's no support for her.”
But others weren't so forgiving. Another student, whose identity was also not revealed said: "It was scary because these girls had to run off to join something that puts a bad name on me and my community.
"I was really scared someone was going to hurt me. I understand she was groomed, but she was a year 11 student and not a little kid."
Shamima, now 21, is currently being held at the al-Roj prison camp, she's still campaigning for the chance to return to the UK and insisted she was just a "dumb kid" who made a "mistake" when she ran off to join ISIS.
Former Home Secretary Sajid Javid revoked her British citizenship on national security grounds shortly after she was found nine months pregnant in a Syrian refugee camp in February 2019.
In February, Begum lost a Supreme Court appeal to return to the UK after her decision to travel to Syria led to her British citizenship being revoked.
A new documentary, The Return: Life After ISIS, will be released on Tuesday where she will detail her struggles being pregnant and caring for her two children while fleeing attacks on ISIS territory.