The Fremantle Building was opened by Edward Duncan-Smith, and features new Science, Design Technology and Art classrooms.
Headmaster Simon Hitchings said: “We are delighted with the new facilities which are the result of the most expensive building project the school has undertaken in its history.
“The school’s development priority since 2013 has been to provide the children and teachers with the best spaces for learning possible.
“This project has delivered Science, Design Technology and Art rooms to be proud of and is a sign of our commitment to the children’s academic development in the skills they will need for the future.
“It is a great pleasure to have the close connection with the Fremantle family maintained as the building originally opened by Lord Cottesloe thirty years ago is now in its completely renovated state opened by his grandson, Mr Edward Duncan-Smith.”