Lay out your decision-making process and use 'If/Then' language. Make sure to demonstrate that you would be aligned with the school's principles and values. You can also use this opportunity to show that you like to develop yourself professionally.
"First, I'd look at what we need to achieve and what the weakest areas were in my last class. If I see that, last year, my students' social studies scores weren't too good, then I'll look into what the deficiencies were and see if there's any improvements that could come from the choice of textbook. I'd ask my colleagues for their opinions, and I'd also look on online communities for ideas. I take a look at each textbook and imagine myself teaching it. It's got to be accessible to the children."