Also, the way that things are presented may have changed so much that we wouldn't understand what the teacher is getting at with a question. My husband and I took a while to figure out my stepdaughter's middle school math a few weeks ago, not because we can't do math, but because we found the way the problems were presented really bizarre. Once we figured out what the teacher wanted, it was simple, but we needed the text book to understand what she was asking.
Also, some things have changed since some of us were in middle school. Eg. Human understanding of the atom was improved a lot between my parents' middle school days and mine. And what my kid will be learning in a few years about the atom is different from what I learned in middle school. I might never have caught up if I hadn't decided to go back to university and study in a field that requires chemistry.