Holidays’ names stricken from next year’s Montgomery schools calendar

Nominally, its a question of numbers. Closing a school on a religious holiday requires a secular rationale in order to pass constitutional muster (ie the establishment clause). For instance, a large number of students and teachers in any given school system are Christian and celebrate Christmas, so there is a secular reason to close on that day. Technically speaking, no "religious" holiday's are given in order to celebrate the underlying religious significance, but for the practical reason that a large number of people would not show up on that day.

In reality, there are probably a number of school systems throughout the US where Muslims outnumber or are as numerous Jews, but those schools don't close on Muslim holidays. In these situations there is clearly a community judgment going on about which holidays should or should not be celebrated.