JFS, Yavneh College and King Solomon High School have agreed to alter their entry rules next year to allow Friday night synagogue attendance to count towards proof of religious practice.
Applicants have to go to a certain number of Shabbat services during the year to fulfil admission requirements.
But the policy this year applied only to Saturday morning attendance.
JFS chairman Michael Glass said the governing bodies of the three schools had now agreed to accept Shabbat evening services as well. "You can go on Friday nights if the synagogue decides to count it," he said. "It should be up to the synagogues to determine."
The issue had been raised by Rabbi Mark Goldsmith of the North Western Reform Synagogue in Golders Green, who said: "I am delighted to hear that JFS and other Orthodox Jewish schools are now counting Friday night service attendance at synagogues.
"I feel that their admissions committees heard a genuine concern last year and have dealt with it appropriately for the good of all."