Funding cuts to schools in Saffron Walden and Newport have become "too difficult to ignore" as head teachers are having to cope with fewer staff, a reduced curriculum and donations from parents.
Plans to build a new primary free school in Saffron Walden have been scrapped as new forecasts demonstrate the project is no longer needed.
More than 7,000 head teachers, including Caroline Derbyshire from Saffron Walden County High School, have written a joint letter to 3.5 million families, warning of worsening budget shortages.
The chairman of Saffron Academy Trust was honoured for his contribution to the profession at the annual Essex Teaching Awards.
The head teacher of Saffron Walden County High School joined 60 other head teachers from Essex on a march to Downing Street to demand better funding for schools.