In Greek and Roman times children and adults often wrote on ostraca (that is, pieces of broken pottery and limestone flakes). They were costless and convenient writing materials. On this flat limestone piece a student practiced letters of the alphabet. S/He did not do so at random but tried to reproduce a nonsensical verse that contained all the letters. Some dots are sprinkled in the text, apparently to divide the "words." In the 5th century CE, the grammarian Hesychius informs us that the ancients considered these nonsensical groups of letters real words, and thus he included them in his lexicon with pseudo meanings. This student forgot at least one letter. His/her style of writing seems to point to an apprentice scribe. Learning the alphabet to perfection and not just by rote was crucial in a world where the letters functioned as mnemonic devises and were also used as numbers.
Acc. 64.2.179. Burton photo M10C 18. Rare Book and Manuscript Library, Columbia University, New York.