CHELMSFORD County High School for Girls will be an academy from next year.
The top performing grammar school will be independent of local authority control and be funded by central government from January 1.
The move has followed months of consultation with staff, parents, students, local schools and the local authority.
It is the first school in Chelmsford to become an academy.
Susan Shanahan, chairman of governors, said: “I am delighted the current governors have seized this opportunity.
“With the support of the parents, my fellow governors and the headteacher Nicole Chapman we will always grasp any opportunity that keeps the school at the forefront of academic achievement.”
Mrs Chapman added: “This is a new chapter opening for our school and we look forward to the opportunities academy status will create.
“We have received support from members of the local community who value the various contributions the school makes to education in the area.”
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