though I am not at business school and my recruiting experience is limited what I do with my job, I agree with River that, with your profile, the hard part isn't necessarily going to be getting into bschool, it's going to be selling to McBain & Co that you have the hard quantitative and analytical skills necessary to credibly convince CXO of Major Corporation Y that you know what you are talking about.
As far as getting into business school, since you undergrad was in History, I think its very important that you do well on the GMAT, particulary the quantitative section, since this will be the prime metric that adcoms are going to have when assessing your ability to handle the math heavy first year course work. As far as taking night courses at Local U, well, let's be honest, if you were a hiring manager at McBain & Co and were comparing a resume that includes teaching over-indulged prepubecents and while taking night classes at Whoville Community College, to someone with 3-5 years of previous consulting/I banking experience, who would you choose? Not to mention, with the measely salaries preschool teachers get paid, you probably wouldn't be able to afford accounting 101
Ultimately you need to ask yourself the question how sure are you that you really want to do MC or I banking? I think the question you are going to have to be able to slickly answer is, "if you really wanted to do I banking/ MC, why did you major in history and then on top of that go and teach?" Not that there is anything wrong with teaching, you just have to think from the firms perspective.