Mark Keary, head teacher at the Bethnal Green Academy where three missing girls go to school, said the pupils would have had no access to Twitter or Facebook whilst at school.
He said there was no evidence that radicalisation of students had taken place at the east London academy.
New footage appears to show three missing London schoolgirls in Turkey during what is believed to be their journey to Syria.
The families of three schoolgirls who fled to Syria to join IS have questioned claims they funded their journey by selling family jewellery.
Relatives of London schoolgirls thought to be in Syria tell ITV News police failed to warn them the girls were at risk of radicalisation.?