Balfour Beatty, which is building £33m Newman RC College under its BSF contract with the local council, hoped to complete the school on time.
But at the last minute project managers had to accept the opening would be delayed by several weeks leaving parents struggling to sort out childcare.
A council spokesman said: “Oldham Council continually monitored and impressed upon Balfour Beatty the necessity to hand over this school site on the agreed date for the start of the Autumn term.
“Despite continual assurances received up to the eleventh hour this did not happen.
“That remains hugely disappointing and unsatisfactory to us. We will be enforcing the terms of our contracts by maximising the financial penalties imposed on Balfour Beatty for this delay.”
It is the second major school project to fail to meet the autumn school start deadline.
Balfour Beatty has also apologised for delays in opening its £40m new build project at Noel-Baker School and St Martins School in Derby.
Construction work has overrun and the school will now be handed over a week late next Monday