Well I believe everything that comes out of a human beings mouth is opinion. There's a probability it's true and a probability that it's false. Both probabilities existing at the same time. People can't make their opinion fact no matter how hard they believe it or how much they want others to.
If everyone realized/believed that, there'd be no problem. Students in classrooms would assign the teacher's opinion to the teacher himself instead of solely to the issue. If Mr. Jones says, "Republicans are greedy," or Ms. Smith says, "Democrats are naive," the student would assign values as such: Mr. Jones + Republicans = value assignment of greedy to Republicans by Mr. Jones. And: Ms. Smith + Democrats = value assignment of naive to Democrates by Ms. Smith.
Or put more simply, your opinion says as much about you as it does about that which your opinion is "about". You + Thing = Opinion.
And like I said, if people realized this, all would be good. Biased teachers could say whatever they want and biased news organizations could do the same. But most people don't do this. They assign the value to the concept itself without filtering it through the person. They minus out the "You" in You + Thing = Opinion.
So, accepting that most people are like this, and assuming you adopt the ethics of equality, I think it's important for teachers and news organizations to either withhold their biases and present both sides (near impossible for many people) or they ADMIT to being biased and have somebody biased in the opposite direction given equal time. ie, they admit that they're applying a good-bad value system to the phenomenon rather than just reporting what is and give someone with a different view equal time.
In the classroom, that can be accomplished by promoting classroom discussion. To be effective, this would require the teacher to again dismiss the absolutism of their good-bad value system, and encourage the equality of opinion in their classroom whether or not it disagrees with their personal value system. Also, this would require the teacher to enforce this equality of opinion among his/her students, regardless if the opinion's split 50/50, or 99/1.
In the media, you could also go the "equal time" route, though I'd *like* to see more observational reporting. With observational reporting you'd have news agencies reporting WHAT'S happening. "This bill was passed, this congressman stepped down, etc." Whenever WHY it's happening is approached, you present both sides. Whenever you approach how it will affect such and such, or in fact whenever you approach anything to do with value judgments, you present both sides.
The ABSOLUTE WORST thing is to have single-sided value-judgement reporting presented as observational reporting. For me, this is the fastest way to lose legitimacy as an attempted reporter of truth, whether you're a teacher OR a news organization.