Parents in east London were reportedly given just three days' notice that a school would be partially closing to allow staff to celebrate the festival of Eid-al-Adha.
Chobham Academy, in Newham closed reception and classes for Year 1 and Year 2 pupils due to a "high number of staff requesting leave for religious observance".
Speaking to The Sun, another parent said it was outrageous they had been given to little notice.
Eid-al-Adha is the holiest day in the Muslim calendar but the date is based on the lunar cycle which means it changes each year.
The Saudi Supreme only confirmed the date of this year's festival on Friday.