A strictly Orthodox girls' primary in west Hendon was forced to close for four days until parents paid overdue fees.
Beis Soroh Schneirer, in Wilberforce Road, faces serious financial difficulties and needs to pay the Nationwide £300,000 in mortgage fees by the end of the month.
It was owed £200,000 in school fees and informed parents last week that it would not reopen until it had received the money.
Lessons resumed on Wednesday after £120,000 in fees had been paid.
Governor Rabbi Akiva Adler explained: "The parent body is not the wealthy part of the community and school fees were being put on the back burner. We couldn't continue without getting the fees, which are already very much reduced.
"We had a bit of a crisis and panicked. We've still got to raise a substantial amount in order to get the mortgage."
The 237-pupil school moved from Finchley Synagogue to its current site in a former industrial warehouse in 2005.