By 1941, his high school education still incomplete, he left Birjand for Tehran. He intended to attend the German-established Tehran Technical School, one of the best secondary schools of that period and learn the German language. He was admitted to this school on the condition that he be demoted two years. Soon in 1942, he and the rest of the family once again left Tehran to move for Gorgan. In 1945, he made a final attempt at completing his high school degree in Urumieh, but he failed. At age 29, following the fall of Prime Minister Mohammad Mosaddeq, Shamlou was arrested for being a member of the communist Tudeh Party of Iran and imprisoned for more than one year.