I'm 90% sure I discovered The Filter while perusing links from Mr Pants. How I found Mr Pants, I don't recall!
roger ackroyd is my hero forever, for finding a beloved poem from my childhood.
When I posted this question, it went unanswered for months and months. Then, out of the blue, roger ackroyd showed up with the answer. I was so excited! It was as if he had validated a part of my life, by proving it existed at all.
The backstory behind that question: I was a depressed kid, and by 8th grade, I had started skipping school. Either I didn't catch the bus, or I went to school and skipped certain classes by going to the school library instead.
Why the school librarian let me get away with it, I'll never know. But I'd end up in her library an average of three times a week, choosing to read magazines and books, rather than going to whatever class I hated. One of those books was the book that roger ackroyd identified for me -- Rhythm Road: Poems to Move to. In particular, I read and reread the poem in my question, about a girl ripping up a love letter and throwing it into the sea, so that her mother could never read it. That poem was short, simple, and sweet, but it meant so much to me. I yearned for a sense of freedom, and for a private life. I was born a very different kind of person than my mother, and I yearned for her to understand that. (Note: Ha, I'm 30 now, and that never happened.)
After roger ackroyd's answer, I filed away the name of the book in my mind, and started looking out for it at used book stores and libraries. I didn't want to order it from someone on Amazon; that just didn't seem right. It didn't exist in any public library I had access to. So I waited for it to turn up.
Finally, only this week, I realized that I could access university libraries, too -- if I just wanted to stop in and make a copy. So thanks to roger ackroyd, and Metafilter, and the School of Library and Information Sciences Library at North Carolina Central University, I now have a copy of my poem. I might frame it.
It's called "Song", by Ruth Krauss.
(And it cannot be forgotten how cool it was, when I discovered one of my friend's mother's was a member. HEEEY ST. ALIA!).