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I think you are absolutely correct that every teacher in a Catholic school is a catechist, whether they recognize it or not. Further, the importance of a teacher’s witness through the lifestyle she leads cannot be overestimated.
Different dioceses have different policies. Some dioceses have it built into a teacher’s contract that they must live a life in keeping with Catholic teaching (or something to that effect). So situations like this actually give them legitimate recourse to dismiss the teacher from her post. But this is not the case everywhere.
Certainly, as a parent you are the primary educator of your child and have the right to expect a solid Catholic education from your Catholic school. These situations cannot always be solved swiftly, however. They can get complicated. But it seems a good sign that both the principal and superintendent are looking into it. You may want to follow up with them at some point to see what other developments there may be.
If it were me, I would consider whether or not the teacher in question is teaching my children specifically, as well as what the alternatives would be. Sometimes we find ourselves in situations where there are no options we would like. If it’s between a Catholic school with some issues, a public school with
more issues, or homeschooling which can be unfeasible for some, then it makes the decision somewhat difficult. But we do the best we can. If the teacher does not “flaunt” her lifestyle, nor encourage children to disregard Catholic teaching, it is possible the children will never even know. Thus, the situation – while certainly not ideal – may still be the best option.
The most important thing is to be a witness ourselves of the Catholic faith for our children. That will influence our children far more than a questionable teacher here and there.