What and on what did the schoolchildren in Athens write?

One of the teachers who taught children to read and write was a grammarist. With his help, Athenian students comprehended the granite of science. It was necessary to write on Diptychs – special wooden plates fastened together. The diptych opened like a book. The edges of the Diptych were protruding. They could be sealed or tied with a rope. The inside of the Diptych was smeared with wax, on which they wrote with a metal stick called Style. The reverse side of the style could erase everything that was written.