You can thank No Child Left Behind (NCLB) for many new regulations and measures school have to implement. Schools and school divisions can use attendance as a measure...so, you better believe they want kids in schools. Also, state funding is often tied to attendance and there are state-level requirements about truancy ("unexplained absences" by some definitions), etc.
I am a public school district administrator and avid camper...I encourage you to work WITH your school to figure out how to do what you want to do as a family and ensure your child has every opportunity to learn what matters most. I also encourage you to advocate for PUBLIC education that embraces what matters most and not the current push for the pursuit of trivia and success on state tests designed to trick 8 year olds.