I think today is the first day that my son asked me about a prescriptive grammar rule. He's in grade two, and he asked me if it was true that you can't start a sentence with and. I asked him why he was curious, and he said that he'd seen it in books but his teacher had said that it was against the rules.
I asked him why his teacher might do that, but he couldn't imagine a reason, so we talked about how kids often tell stories with and between every "sentence" and I asked him how it sounds if you use the same word(s) too many times. In the end, we agreed that you can start a sentence with and but that you just shouldn't do it too much.
Which seemed to satisfy him, until he added, "but you can't have two ands in the same sentence, right?" So we got to look at the difference between coordinating clauses and phrases, and he had no trouble seeing the difference once it was brought to his attention.
If a bright seven-year-old can notice a discrepancy between what he's being told and what he sees, and if he can understand the facts of grammar with a little Socratic questioning, why do we teach all these fake oversimplifications?