Pepin the Short (or The Breif) holds another distinction over his more famous son and father: he was undefeated in the field of battle. I myself love Pepin and think he's one cool cat, but unfortunately there are a number of considerations that textbook and school program writers have in mind when choosing what to include and what not to include.

Unfortunately, Pepin never won a decisive victory against an easily vilified foreign foe like his father Carl did at Tours. Plus, he chose not to occupy Italy after defeating the Lombards (thus leaving no permanent imprint for prolific Italian chronicles beyond confirming the Pope's territorial jurisdiction in modern Lazio, and again here he's often upstaged by his Son's coronation as Emperor, leading many to believe the pope never exerted temporal power prior to that point). Ruling successfully and efficiently putting down revolts won't get you exalted by history books, unfortunately.

Further, in addition to his conquest of Italy, Charlemagne's Saxon Wars over the course of three decades brought Saxony, Thurungia, Bavaria and Carinthia into his Empire's fold (I.E. most of modern Germany). The crowns of Italy, Germany, and France can be traced to him: that's three countries which have one person to conveniently start their medieval history with.