Parents of some Sikh students approached the local administration on the issue after the school refused to withdraw its March 2 verbal order.
"We have given a number of representations to the school principal since the ban was imposed, but there has been no response so far. The turban is part of the Sikh religious attire, how can a school impose ban on it," a parent said.
He said the students were wearing full-sized turban in the school in the previous years.
"We have given enough time to the school to resolve the issue, but it's adamant on the ban. The principal is now saying that from the next session the school will allow students of Class 11 and 12 to wear turban," the parents said.
Shimla Deputy Commissioner Onkar Sharma told IANS that a complaint was received from parents.
"We have taken a serious note of it and will take appropriate action, if the school doesn't sort out the issue on priority," he added.
School principal John Bosco said: "I had only asked a Class 12 student on the first day of the session (March 2) why he was not wearing a 'patka' like other boys. I called his parents and the matter ended after I met his parents. I allowed him to wear whatever he wanted."
"Now a non-issue is being made an issue," he added.
St Edward's School has been a prominent boys' school in Shimla since March 9, 1925, in the Milsington Estate. Brother J.C. Doheny was its founder principal.
Besides Mr Ansari, the school boasts of alumni like former cricketer Kapil Dev, former Punjab Police chief K.P.S. Gill and union minister and former chief minister Virbhadra Singh.
State Bharatiya Janata Party spokesperson Ganesh Dutt said in a statement that the school decision was unfortunate and it should immediately take back its order.