I can assure you that Christian colleges have textbooks for their religion courses. There are all kinds or choices available for books that fit the theology of the institution.
I don't dispute that. What I was saying is that because there is so much out there in terms of various theologies and "truths" that it would cut down on confusion if you taught a course outlined in a book that was straight from the bible.
Well, that is what they do. Textbooks on systematic theology, New Testament Survey, Old Testament Survey, Christian Ethics, Romans, etc., etc.; are developed by authors who use their interpretation of Scripture and what other authors have written on the subject.
You would look at the author(s) to determine what their framework is. For instance, if the author was a professor at the Dallas Theological Seminary, you could know that it was a fundamentalist evangelical perspective.
A good instructor at a Christian college would be willing to point out to the students any differing interpretations he had with a textbook.
But to use no textbooks at all, the school is proclaiming that the only interpretation that matters is their own local interpretation. Not a good approach, IMHO, given two thousand years of Christian scholarship.