The head of Glebe Primary School, in Southwick, has resigned, citing the "impossibly stressful" pressures of the job coupled with the lack of funding.
Jo Kelly has been part of the Glebe team for four years, moving from Bolnore Village Primary School, to take over from Ann Walton.
In a letter to parents she said: "After 15 years in education, I do not feel I can carry on in our broken system.
"I came into this profession to give children the best life chances possible and I do not feel that I am able to do this any longer.
"The high stakes accountability system in place across the country means that we, as a profession, are taking the excitement and creativity out of teaching and learning.
"At Glebe, the fantastic staff team do everything in their power to give our children the best experience possible but even over the four years that I have been here, the pressure has increased and we are putting more and more pressure on staff and children to reach more and more difficult goals.
"I think this is unacceptable and don’t wish to see our children go through this anymore.
"The pressures from testing, the changes to the curriculum, league tables, Ofsted and the government have made it impossibly stressful.
"This is now coupled with a lack of funding to give children the very best start that they deserve – we are having to do more with less.
"Over the next few years, there will be some very difficult decisions to be made about staffing and this will again have a negative impact on our children."
Shane Hales, chairman of governors at Glebe, said Miss Kelly's last day would be August 31.
He said the governing body had already met to discuss recruiting her replacement and hoped she or he would take up their post in january 2019.
An interim headteacher, supported through the local authority, will be put in place from September.
Mr Hales added: "Everyone will have the opportunity to say goodbye and thank you to Miss Kelly at the end of the summer term. In the meantime, on behalf of the Governing Body, I would like to thank Jo for her excellent contribution to Glebe Primary School and extend our very best wishes for her in the future."
Miss Kelly added: "The thing that makes me most proud of my work in education has been seeing a generation of children develop and turn into fantastic young people.
"It is with great pride that I come to school every day and work with the unique Glebies and I am so sad that I am giving up the career that I loved and have worked so hard for.
"However, I do not think the education system is fit for purpose.
"My role seems to be less about giving children rich and diverse experience and more about making sure they tick all the boxes required for a narrow testing and assessment system."