A battledore was a child's horn-book.
Horn-book (from E-NED):
A leaf of paper containing the alphabet (often with the addition of the ten digits, some elements of spelling, and the Lord's Prayer) protected by a thin plate of translucent horn, and mounted on a tablet of wood with a projecting piece for a handle. A simpler and later form of this, consisting of the tablet without the horn covering, or a piece of stiff cardboard varnished, was also called a battledore.
1693 - Phraseologia Generalis; A Full Large and General Phrase Book,
see below from E-NED