Unknown militant threw the bomb at the Askari Public School and College in the Shabqadar area of provincial capital Peshawar. The militants fled after the attack.
The explosion resulted in the death of school teacher and injured two children, Dawn reported.
He said the school had received letters a month earlier that it will be attacked of the western style student uniform was not replaced with salwar kameez.
Chief Minister of Khyber-Pakhtunkhwa province Pervez Khattak condemned the attack and sympathised with the families of those targeted.
The party had objected to pictures of girls without dupatta (traditional scarf) at their identity cards, saying 'good morning' like greetings and pictures of Christmas cake, Cross emblem etc in the syllabus books.