The OP said the study was of public schools. If it were private schools, that's all fine and dandy.I'm assuming some of the schools are private, which is how it is legal.
That's the part I don't know how it is legal. Public schools are an extension of the state, since they are being run by the state. You can't teach one religious perspective as fact; that's clearly a violation of students' first ammendment rights.And even public schools are known for being subject to twisted state laws that taint, distort, and even fabricate things to make their side seem correct and allow for things that are indeed clearly unconstitutional (such as how many states have laws in place to allow for discrimination against GLBT students, or allow for the teaching of religious mythos as science fact without any possibly consequences).