An Etymological Dictionary of the German Language/Pennal
Pennal, n. ‘pen-case,’ ModHG. only, formed from MidLat. pennale; with this comp. Pennal meaning, ‘grammar-school, high-school, pupil.’ To the students at the university the school might seem as a huge array of pen-cases, and “in jest the freshman too was called a ‘pen-case,’ probably because he attended lectures regularly, and so carried his pen-case with him.”