Having previously represented the Germany U17 and Germany U18 side, Compper was called up by Germany U20 for the first time, making his debut against Italy U20 on 16 February 2005. Three months after making his debut, Compper was called to the Germany U20 squad for the FIFA World Youth Championship in Netherlands. After appearing twice as a substitute bench in the first two matches, he played his first match of the tournament, where he came on as a second–half substitute, in a 1–0 loss against Argentina U20 on 18 June 2005. Compper started for the first time in the tournament, as Germany U20 lost 2–1 to Brazil after the game went to extra time, eliminating the side from the competitions. He went on to make eleven appearances for the U20 side.