The story is about a young boy who receives a silver ball of yarn or string (I think from some sort of magical fairy that visits him at night), and this ball of yarn has the ability to fast forward time. If he pulls a bit of string time goes forward. He is warned to use this gift carefully, but of course he doesn't. So he ends up pulling way more than he should have ever pulled, and he becomes and old man, his mother is dead, and he's devastated by this. He is then visited by the fairy (or w/e) again, and time is reset.
Anyway, none of my google searches have revealed a good result, and maybe someone else here has read/heard this story (I think we read it in fourth grade) and knows what I'm talking about.