Disagreements With Parents Can Be Fruitful, Arguments Not So Much
In our society we often confuse disagreements with arguments, but the aren't the same thing. A disagreement with a parent can be fertile ground to find solutions to problems getting in the say of teaching a student, but arguments with parents often end up in heightened emotions, and are, by and large, a waste of time.
Disagreements occur when you and the parent hold different views about a specific issue. For example, a parent may have some concerns about too much homework, and broach that subject at a parent-teacher meeting. You, as the teacher disagree. That's not necessarily a bad thing, provided both parties can stay on topic, identify why the parent is concerned, and use the disagreement as an opportunity to explore particular issues relevant to the student's learning.
In a well handled disagreement, teachers can LEARN important things about the student that can help the student, because the parent knows the child from a different perspective. Even if that perspective isn't consistent with the teacher's advice, there's opportunity to learn, and problem solve with the parent. If that disagreement never occurred, important information might be lost, and neither party would realize it.
Disagreements are differences of opinion. The emotional attachments to the disagreement don't get in the way of constructive information sharing.
Arguments are a bit different, and usually include a difference of opinion. One difference is that the parent attaches a high degree of emotion to the opinion, as might you, as the teacher. Parent arguments tend to lose the original issue, as each party tries to win the argument, and in the worst situations, emotions escalate and one or both parties can get abusive, and insulting. One example: During a parent-teacher meeting, the parent expresses the strong opinion that teachers are overpaid. Not only is this not an issue related to the particular child, but trying to argue that the parent's opinion is wrong will just escalate the discussion.
Staying Out of Arguments With Parents
It may seem to you, as a teacher, that you have little control over whether a disagreement turns into a "waste of time argument", but that's not true. By refusing to directly engage the parent over an issue that is not relevant to the child, and is often something neither you or the parent can do something about, you can exert control over how the conversation goes. Don't get suckered into arguments that are irrelevant, and keep in mind that arguing is simply not likely to end up with either party changing their opinions. (see Teachers Need To Pick Their Battles With Parents)