The school attended by three teenage girls who are believed to be heading to Syria had "no evidence" they were being radicalised or might abscond - despite another pupil leaving to join Islamic State in December.
Classmates of Shamima Begum, 15, Kadiza Sultana, 16, and Amira Abase, 15, have now returned to Bethnal Green Academy following half-term.
The trio disappeared last week - two months after a fellow pupil is thought to have left to join IS in Syria.
Principal Mark Keary revealed that police had spoken to Shamima, Kadiza and Amira at the time and found "no evidence that the girls were at risk of being radicalised or absconding".
Staff at the school were briefed by police upon their return to work, Mr Keary said, while all pupils have been offered agency support.
He added that social media was "strictly regulated" at the school - with no access to Facebook or Twitter.
This follows the revelation that a tweet from an account under Shamima's name was sent to Aqsa Mahmood, who left Glasgow for Syria to be a so-called jihadi bride in 2013.
The latest developments came as six French citizens had their passports confiscated after allegedly planning to travel to Syria, according to a security source.
The right to remove passports was introduced there amid a raft of new counter-terrorism laws in November.
Meanwhile, officers from the Metropolitan Police have now arrived in Turkey as the search for the girls continues.
Relatives of the trio have made emotional pleas for them to come home.
The three girls were last seen on Tuesday morning as they left their homes, telling their families they would be out for the day.
They are thought to have boarded a Turkish Airlines flight at Gatwick, which landed in Istanbul on Tuesday evening, with the intention to cross into Syria and join IS.
The father of Amira, Abase Hussen, said his family was "completely different now".
"We are depressed, and it's very stressful," he said. "The message we have for Amira is to get back home. We miss you. We cannot stop crying. Please think twice. Don't go to Syria."
