Undeniably, there are good and bad parochial schools just as public schools vary in their excellence. It is unrealistic to make a broad general statement that parochial schools are better than public schools. In order to decide whether your daughters could receive the same education at a public school as at the school they are now attending, you need to compare the two schools. Look at the curriculums and decide which one best meets your daughters' needs. Compare the copyright dates on textbooks. While old math and English textbooks can be good instructional tools, old history and geography books will not give your children a solid knowledge of recent events and boundary changes. Consider also such things as class size, achievement test scores, the teachers, and the emphasis on order and discipline.
There is one additional factor to think about. The parochial school is giving your children a religious upbringing that cannot be duplicated at a once a week religion class. Furthermore, they are having the chance to be with a group with similar values and be part of a faith community.