Neighbours of Pelham Primary School, in Southey Road, were informed construction work that started on Monday will last for more than a year.
A letter to residents from contractors Balfour Beatty Construction stated three parking bays on either side of the busy road will be suspended, there will be a new crossing over the pedestrian footpath and the building site will be set up over the Easter break.
The three-storey classroom extension, library, toilet facilities and remodelling of play areas and landscaping is part of the council’s investment in education.
Work is expected to take 76 weeks to complete.
Southey Road resident James Lawrenson said: “It seems like a long time to be doing work for.
“So far there hasn’t been too much noise and disruption so hopefully it stays like that.”
Prior to work starting, pupils celebrated with an Easter egg designing competition.
A meeting on Wednesday, April 2, saw funding of £1,134,483 of Section 106 money approved for expansion of primary schools across the borough.
The cash boost is the latest in the council’s £80m plan for primary schools in Merton, to create 4,000 additional school places.
The council’s cabinet member for education, Councillor Martin Whelton, said: “I think it is important for this to happen because we have seen a 39 per cent increase in birth rates.
“As an authority we have been actively addressing this – we have a duty to provide local schools to local people.”
Parents will discover whether their children have got their desired primary school places for September this year on Wednesday.