JFS has called a halt to its popular bar- and batmitzvah ceremonies, saying the decision was taken because of pressure from local communities to hold the celebrations in synagogue.
But a senior United Synagogue rabbi has cast doubt on the explanation, suggesting that the move resulted from new entry rules that prevent schools from knowing whether pupils are halachically Jewish.
JFS headmaster Jonathan Miller said that members of the local community had "voiced concern that pupils were having their bar- and batmitzvahs at JFS, and not within the community.
"We thought about it long and hard and have decided not to continue having the celebrations here. It will make some people unhappy but unfortunately you can't get it right for everyone. It's the only reason why we decided to cancel the bar- and batmitzvahs here. It is not connected to anything else."
But Rabbi Yitzchak Schochet, of Mill Hill Synagogue, believes the change is due to last year's Supreme Court ruling on Jewish school admissions. Schools are no longer allowed to carry out checks on applicants' Jewish status.
Rabbi Schochet - who chairs the US's Rabbinical Council - said that, based on information he had received from those involved in religious services at JFS, the school's explanation "doesn't quite wash with me.
"Why now? After how many years? And how many kids is it really stopping having barmitzvahs in shul? I still had 33 barmitzvahs last year, 37 the year before that and bookings are now running all the way through 2013."
Pupils who hold their celebrations at JFS, he said, "are otherwise not inclined to have it in a shul and will now not likely have one altogether".
Malcolm Gordon, chairman of Yavneh College in Hertfordshire, said the school had never held bar- or batmitzvahs on the premises.