My church requires that before people get married, they attend a session on "Natural Family Planning." This method basically involves learning to track your fertility using temperature and other physical symptoms, then abstaining from sex during your most fertile periods as a means of controlling family size without using artificial birth control.
Much of the session was devoted to statements about how incredibly effective this method is. Which, ok, maybe, if you actually follow it. But the likelihood of anyone actually being able to follow it regularly enough to maintain a typical family size was undermined a bit by two facts: (1) Our NFP teacher was pregnant with her 7th child; and (2) A guy in our class mentioned that his parents had taught NFP. He later mentioned that he was one of 12 (!) children.