The point of a debate should not be to "win" or to convert everybody to your way of thinking, but to further the development of your own opinions and perhaps further the development of the other persons too. There is no winning or loosing in a debate as long as you personally gain something constructive out of it (even if all that happens is that your current opinions are just further reinforced).
So when you debate something with a teacher, don't be stubborn- you may think you are right, but even if you are it still helps to be open to the other persons opinions. At the very least you can try and understand how the other person formed their opinions (even if you don't agree with them).
Teachers are not perfect, but also give them credit that their lives are often very hard (when you finish school & go home to eat and relax with your family, they will still be working etc). From what i've heard teaching is a very difficult job. So if the teacher doesn't want to debate with you, also take into consideration that they may not have the time to debate with you or may not have the energy to etc. When they have a break time, they may actually want to have a break time. Don't take it as the teacher not wanting to hear your opinions or listen to what you have to say etc. Even simple subjects can take a long time to debate before a conclusion is understood & accepted.
So be respectful. Listen to what you yourself are saying as much as what the teacher is saying. Don't be stubborn and don't try to debate with the aim of "winning", but instead rather with the aim of furthering your own personal understanding & development. Make sure your sources of information are good & legit (not wikipedia...) and think through your own side of the debate thoroughly before approaching someone to debate with.
And when you are debating with a teacher, while they are a great sourse of wisdom, experience & information, teaching is a very stressful and full-on type of job, so make sure you respect your teachers personal time & space and don't hassle them over something that they are doing you the favor on etc

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