That is not what the establishment of religion means. The Bill of Rights forbids the "establishment" of a national religion, nothing more. Establishment would be the creation of a new religion through legislation. Passing legislation based on the teaching of religion is not the establishment of a national religion.
>>The Bill of Rights forbids the "establishment" of a national religion, nothing more.<<
To be more precise, what it forbids is the federal government messing around with previous establishments in individual states, hence the phrase "no law respecting an establishment of religion." When you put the text into a historical context, and realize that there were many state establishments, you realize the framers simply wanted to keep the federal government out of the state house.
Effectively, that means no federal establishment, but the clause has been misunderstood from day one. Most of the misunderstanding is intentional for political purposes.