We should certainly always avoid sending Bahá’í children to orthodox religious schools, especially Catholic.

If you feel convinced your son will really benefit from going to Father Flanagan’s school you could send him there. But in general we should certainly always avoid sending Bahá’í children to orthodox religious schools, especially Catholic, as the children receive the imprint of religious beliefs we as believers know are outdated and no longer for this age. He will especially pray for the solution of this problem.

(From a letter dated 30 May 1947 written on behalf of Shoghi Effendi to an individual believer)

http://reference.bahai.org/en/t/c/BE/be-135.html