Karen Edwards, who joined Sacred Heart primary in Greys Hill in 2006, has been appointed head of the Heights, a new free school in Caversham.
Mrs Edwards, 46, said: “Sacred Heart has been a part of every aspect of my life for seven years and I’ve enjoyed everything about it. It’s a great place and the pupils, staff and parents have all been fantastic.
“My new job is a very rare opportunity to grow and develop a new school from the bottom up. This kind of opportunity doesn’t come around very often.”
Mrs Edwards is well known at Sacred Heart for her fund-raising activities, including getting pelted with wet sponges in the stocks at the school fair. She has also been at the forefront of a campaign to get a pedestrian crossing installed on Greys Road outside the school.
Morag Stewart, who chairs the governors, said: “We will be very sorry to see Karen go after seven very successful years at the school but understand that she has been presented with a rare career opportunity and fully respect her decision.”
Mrs Edwards will remain at Sacred Heart until the end of the spring term and a new headteacher will be appointed for the start of the next academic year.
Rachel Gavin will be acting headteacher between April and September.
The Heights, which is funded by a £220,000 government grant and will be run by a body of governors, is set to open in September with two reception classes of about 25 pupils each.
The school hopes to add two new reception classes each year, with the aim of reaching full capacity of 350 pupils by 2020.