I think the following should be obvious:
Different kids (and adults) go off the derech for different reasons. Some kids go off the derech because they are too sheltered and feel stifled by frumkeit. Some kids go off the derech because they are allowed too much involvement in the non-Jewish world. There are many, many reasons that children go off the derech and beyond free will there is no one reason that is relevant in every case.
Any uniform policy is going to have negative unintended consequences. School’s are constricted, for the most part, to uniform policies, but parents are not. Therefore, parents can and must alter their policies to fit the personality and circumstances of each individual child.