A teaching union estimates up to two thirds of physical assaults on school staff in Nottingham are not being reported.
The NASUWT says physical and verbal attacks are on the decrease - but many teachers do not report incidents when they do happen.
It is thought that many teachers do not report abusive behaviour because they are worried it will reflect badly on them.
The union is calling for more action against pupils who assault staff.
Permanent exclusion
Graham Byers, the Nottingham officer of the NASUWT, said: "There is a real possibility that these incidents are not always recorded.
"Sometimes the head teacher may not have the right forms available.
"Other times the head teacher may think the incident will reflect badly on the school if he has to involve the health and safety officers of the Education department."
He added: "We are pressing for a zero tolerance on physical assaults and feel the city council have listened to our concerns."
Nottingham Local Education Authority say they take assaults against staff extremely seriously and will always prosecute.
They are also expanding their provision for excluded pupils and head teachers are told permanent exclusion must be considered for physical assault