But do you see that your relationship with your spouse DOES affect your kids? And then your kids go to school, and the teachers deal with them, etc. etc. Everything is interconnected, whether you want to believe it or not. If Johnny's dad is cold, aloof, and indifferent to Johnny's mom, and Johnny's mom treats Johnny's dad like a child and doesn't respect him, then how do you think Johnny will treat others (at school and otherwise?). Then it becomes a school problem. Think of John and Kate Gosselin, and the problems that their kids probably have now from witnessing a very unhealthy marriage.
I don't look at it as "marital advice" from the school. I actually look at it as "common sense". Unfortunately, not everyone possesses common sense- in fact, it's getting less and less these days. But, what you do at home affects what your kids do in school. I know it, because I teach. I see it every day, even in my age group!