After attending an elementary school for four years, at about age ten students were tested to determine what type of future career they would enter: either professional or technical. Those destined for professional careers, such as law, medicine, or academics, began a nine-year course of study at a Gymnasium in preparation for entering a university.
A German Gymnasium, spelled with a capital G and pronounced "gimnahsium," has nothing to do with sports. It derives from the Greek word for "school." In Germany and other central European countries it was and still is roughly equivalent to an American academic prep school. In Heisenberg's day most Gymnasiums were called "humanistic." The Humanists were scholars of classical literature. The Gymnasium placed a heavy emphasis upon classical Greek and Latin. This classical education aimed to produce not only educated scholars but also but also useful contributors to German culture, combining rationality with high cultural scholarship. Today, Gymnasium students may focus instead on science, math, and modern languages, but in Heisenberg's day these subjects received only minimal attention compared to classical languages.
Students received intensive written and oral exams at the conclusion of their Gymnasium studies. Those who passed received a "leaving certificate" (Abiturzeugnis), which entitled them to admission to a university for their professional training.
At the conclusion of their Gymnasium studies students were, and are today, at an age and an educational level roughly equivalent to the end of the sophomore year of an American college. Today they graduate from the university with a "Diplom," the equivalent of an American master's degree, and then go on to doctoral studies.
In Heisenberg's day the emphasis in the sciences was on research from the very start of university studies and the goal was to gain a doctorate, which was necessary for a career as a professor in any field. This required a published paper in a professional journal and a graded final oral examination. Bright students, such as Heisenberg, could obtain a doctorate in the minimum time of three years, but such students were usually not yet at the level of American doctorate in science. For this reason, future professors usually had to obtain a further degree, the Habilitation, which was required for teaching at the university level. Following the doctorate, the future professor obtained a temporary assistantship in the institute of a professor in their field. The assistant usually taught a minimum of one seminar, devoting the rest of his time to research leading in six years or less to a major publication that he could submit for his Habilitation (most of the candidates were indeed men). In a process roughly equivalent to the granting of tenure at American universities, the candidate's Habilitation thesis and other qualifications were carefully scrutinized by the faculty, and the candidate had to present a public lecture followed by a public oral exam in his field. Once "habilitated," the candidate was deemed qualified for permanent appointment as a full professor at any German university.
Having surmounted the hurdle of Habilitation, the future professor could begin lecturing at the university even before receiving an appointment. While waiting for an appointment, the candidate could support himself by offering "private lectures" for which the students paid fees directly to the lecturer. Such a lecturer was called a "Privatdozent." After appointment to a "public" teaching chair as a full professor, the new professor was now an employee of the state, since all universities were, and still are, state-supported institutions.