The new class - at St James Primary School in Coldwaltham - is now home to the school’s reception children.
A school spokesperson said: “The feedback from the children, teaching staff and visitors has been really positive which has made all the hard work worthwhile.
“This extra space has also enabled us to reconfigure other classrooms to make best use of space to support our continuing growth in pupil numbers.
“We are very grateful for the generous legacy left to the school by Mrs Marigold Allen, which made the creation of the new classroom possible.
“Mrs Allen was a resident of Hardham and wanted to contribute to the school community by providing a place where children could thrive and learn.
“The new classroom will certainly allow this to happen and we are planning a wonderful opening ceremony for the building which will be called ‘The Mari Allen Building’.”