In addition to working as a regular Ministry of Finance official, Soeda gave a course in economics at Tokyo Imperial University, Tokyo Senmon Gakko (present-day Waseda University), Senshu School (present-day Senshu University), and Gakushuin (at Senchu School, which was established by his former teacher and boss Inajiro TAJIRI, he worked with his colleague, Yoshio SAKATANI, who entered the Ministry in the same year, and they were in charge of classes in history of commerce).
添田は現役の大蔵官僚としての生活の傍ら、東京帝国大学、東京専門学校（現・早稲田大学）、専修学校（現・専修大学）、学習院などで経済学を講じており（恩師・上司であった田尻稲次郎が設立した専修学校では、同僚・同期の阪谷芳郎とともに出講し商業史などを担当）。