Right, I got it the other way around. This is the excerpt from the book:

Accordingly, Ludwig was sent, not to the grammar school in Vienna that Paul attended, but to the more technical and less academic Realschule in Linz. It was, it is true, feared that he would not pass the rigorous entrance examinations set by a grammar school, but the primary consideration was the feeling that a more technical education would suit his interests better. The Realschule at Linz, however, has not gone down in history as a promising training ground for future engineers and industrialists. If it is famous for anything, it is for being the seedbed of Adolf Hitler’s Weltanschauung. Hitler was, in fact, a contemporary of Wittgenstein’s there, and (if Mein Kampf can be believed) it was the history teacher at the school, Leopold Pötsch, who first taught him to see the Habsburg Empire as a ‘degenerate dynasty’ and to distinguish the hopeless dynastic patriotism of those loyal to the Habsburgs from the (to Hitler) more appealing Völkisch nationalism of the pan-German movement. Hitler, though almost exactly the same age as Wittgenstein, was two years behind at school. They overlapped at the school for only the year 1904–5, before Hitler was forced to leave because of his poor record. There is no evidence that they had anything to do with one another.

Wittgenstein spent three years at the school, from 1903 to 1906. His school reports survive, and show him to have been, on the whole, a fairly poor student. If one translates the five subject-grades used in the school into a scale from A to E, then he achieved an A only twice in his school career – both times in religious studies. In most subjects he was graded C or D, rising to a B every now and again in English and natural history, and sinking to an E on one occasion in chemistry. If there is a pattern to his results, it is that he was, if anything, weaker in the scientific and technical subjects than in the humanities.