Well, the first thing would be real, accurate sex ed for all students (home- and private schoolers included) to cut way down on "oh shit she's pregnant, better get married" scenarios - that'll nip an awful lot of bad marriages in the bud right there. But like anything that would actually make things better, it's easier said than done, politically speaking.
Beyond that, some kind of premarital counseling is definitely a good idea; the problem would be that if there was suddenly a huge demand for it because it was no longer an optional thing couples sought out, quality would inevitably suffer.
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