A school district has been sued for something like that. In Church of God, Etc. v. Amarillo Indep. Sch., 511 F. Supp. 613, plaintiffs successfully sued the school district "to enjoin the enforcement of the Amarillo School District's absence policy which limits the number of excused absences for religious holidays to two days each school year", where "A fundamental tenet of the Church of God is that members must abstain from secular activity on seven annual holy days". The school district imposed an absence polity where "School work missed may be made up whether an absence is excused or unexcused", and "Excused absences shall be granted to students for a maximum of 2 days for religious holidays in each school year". The court concluded that "This policy poses an unquestionable burden on the Plaintiffs' religious belief", and "This burden is not ameliorated by the make-up work provision. The provision does not require a teacher to evaluate the work made up. It in fact directs the teacher to enter a zero for that work". In this case "Summary judgment is granted and judgment rendered enjoining the enforcement of the Amarillo Independent School District's excused absence policy insofar as it limits the number of excused absences for religious holidays". This is not a matter of religious discrimination, this is a First Amendment issue. The policy is in violation of the Free Exercise clause.
Eliminating spring break per se is not a problem: doing so and providing no excused absences is the problem. In the above case, there was clear a religious principle of the church to the effect that one must be off the clock on the holiday. As far as I know, there is no requirement to abstain from work or school on Shrove Tuesday, Ash Wednesday or Good Friday. Nevertheless, in recognition of New Jersey state law which allows any student to take off a religious holiday – including Shrove Tuesday and Ash Wednesday, and dozens more – the Board of Education has prepared a list of such holidays, which includes Wiccan, Hindu, Baha'i, Jewish, Zoroastrian, Church of Scientology (and so on) religious holidays.