Kingston Council leader Kevin Davis says pupils at the new Kingston Academy free school will have 18 months of building work around them after the school opens.
In September 2015, 180 year seven students are due to begin their studies at the converted North Kingston Centre in Richmond Road.
Planning permission has still not been granted for the school which will eventually have 900 students.
Coun Davis said: "The reality is that school will have a significant amount of building work going on at the back of it for about 18 months after it opens.
"It does now look like they will get the school open by September 2015, but they have got an awful lot of work to do.
"They have got to consult before they put an application in, and that will probably have to wait until September now. I've seen a timetable and it's a bit sloppy."
Are you a parent of a child heading for Kingston Academy? Call the newsdesk on 020 8722 6318 or email firstname.lastname@example.org