It wasn't a stone that was in classrooms for kids. That's ridiculous. It was a decree that priests put out extolling the virtues of Ptolemy V, the Greek ruler who was over Egypt at the time. Sure. Because this Greek rule was over the Egyptian citizens, there was a need for there to be multiple scripts included in the decrees that were sent down from on high. There are a bunch of these decrees that include hieroglyphics, Egyptian demotic text, and Greek script, which allowed for the translation of hieroglyphics through the Greek, which previously had been something we weren't successful in doing.