Confirmation bias is one of the many cognitive biases that affects the way we view the world. We tend to look for (and trust) information that confirms our own beliefs: this is the confirmation bias in action! This is one of the more significant cognitive biases because it can distort evidence-based decision-making. As an example, let's say, "brussels sprouts are bad." If you already don't like brussels sprouts, it's easy to take this statement at face value and agree with it. However, brussels sprouts aren't inherently bad: they provide important nutritional value, even if you don't like them! Liking the way brussels sprouts taste is completely subjective but them being healthy is not. This is where confirmation bias gets tricky when researching topics for school.
Let's say you're researching year-round school. The way you pose questions will change the results you would find. You believe year round school is bad and to support your argument, you search, "why year round school is bad." This kind of search will give you results that learn towards your biases, and the same goes for searching the opposite ("why year round school is good".)
This may not seem like a bad thing, after all, you did get the answer you wanted... but is it right? For the most part, no. You only received information from one side of the story. Biased and one-sided arguments tend to be based in opinions rather than fact. Since you searched "why year-round school is bad" and chose a biased article as a source for your paper, you are only looking at one side of the argument and likely disregarding half of the argument. This makes you a biased source, and totally unreliable.
So, how do you avoid being biased? It's not easy, but the most important thing to keep in mind is to be neutral. Rather than asking why year-round school is good or bad, search for statistics and facts on the topic. One of the first things you could look for is if grades, attendance, or retention had changed. That can help you solidify your opinion and then you could move on from there to things like professional opinions, first-hand accounts from students/teachers/parents, and more!