Not once, in my education both in high school AND college, was I told that the Big Bang is the singular explanation for the creation of the universe.
GotoWar is making some excellent points, and they're consistent with what I have learned in school. Now, I agree some teachers may impose biases just as some students may assume biases based on their beliefs.
One thing we all need to realize is that not everything you learn in school is correct and not everyone is taught by the most qualified individuals. School, particularly high school, is a guide. Students need to be more proactive in finding their own facts and making their own decisions. Science class should, and I think as a majority does, teach scientific facts as they are seen, without any bias or faith-based speculation. Ultimately, the decision is the students to determine what they believe, but we have a certain precident in this country to teach what can and is observable and scientifically tested.
The biggest myth about a theory is that a theory is a scientists "guess" about what could have, or might have happened. It's not a guess, it is a scientific process of discovery and observative. If it can't be tested or at least studied, it would never be a theory to begin with. Hence the reason intelligent design is not a theory. The Big Bang itself is a theory because it is the scientifically explanable reason for the universe, it's motion and its size.