31 The believer has an absolute right to profess his Faith and live according to its dictates. Laws which impede this profession and practice of Faith are against natural law. Parents who are earnest and conscious of their educative duties, have a primary right to the education of the children God has given them in the spirit of their Faith, and according to its prescriptions. Laws and measures which in school questions fail to respect this freedom of the parents go against natural law, and are immoral. The Church, whose mission it is to preserve and explain the natural law, as it is divine in its origin, cannot but declare that the recent enrollment into schools organized without a semblance of freedom, is the result of unjust pressure, and is a violation of every common right.
Source: Mit Brennender Sorge (Vatican.va)