Can you distinguish which media discourse is right?

When I was in press in my university, my senior said we've learned media should be just and fair to all in schools but it's not in reality. I was surprised and I had a chaos in my point of view.
To my students I'm not sure how they are taught about media whether it's just or not. If they are taught, it's right or fair to the fact, how would we help them know the unfair media or media discourse, furthermore the power in discourse? If they are taught, it's not all right, what should we do? How can we help them to understnad the media (discourse) and power?