Grange Primary School just off Tower Bridge Road is celebrating the completion of its £8 million new building as it expands to become a two form entry school.
The primary school will in future take in 60 pupils a year to meet the growing demand for school places in Bermondsey.
To accommodate the extra pupils, the Victorian school has been refurbished with new satellite classrooms, a designated early years playground and a brand new building with school hall, kitchen, nursery, library and office accommodation.
At the heart of the new school building is the double height Albert McKenzie Hall. Named after a local World War I hero, the hall now provides enhanced dining facilities and space for the whole school to come together for assembly.
"It is great to see another one of the schools that we have invested in as part of our expansion programme welcome children back into their renovated classrooms," said Cllr Victoria Mills, cabinet member for children and education.
"It has been fantastic to hear from parents, teachers and the children themselves about how the improvements to the school have had such a positive impact on school life already."
Co-headteacher Maddy Webb said: "I know I speak for the whole Grange community when I say that we are all thrilled with the work that has been done on the school and we wish to thank everyone involved for their commitment to improving opportunities for Southwark children."
Diana Valcheva, co-headteacher, added: "We are all thrilled that our children will be able to enjoy the exciting and stimulating learning environment they deserve."
Grange was rated 'good' by Ofsted in its latest report published this autumn.