This paper reports an experiment about interactive humanoid robots immersed in real human society with a com-munication task: language education. With recent robotics technology, a humanoid robot can provides an abundance of non-verbal information as well as vocal information, which enables us to smoothly communicate with it. We believe that these robots, partner robots, are advancing toward participation in human society. A humanoid robot named Robovie has been developed as such a partner to humans. It autonomously interacts with humans by speaking and making gestures with implemented child-like interactive behaviors. In addition, it employs a wireless system to identify individuals and adapt its behaviors to them. We performed an exploratory experiment to investigate the long-term relationships between humans and the partner robots that have a communication task. In the experiment, students in an elementary school interacted with two robots over 18 days. Each robot spoke in English with the Japanese students. We expected the students to form stable relationships with the robot by way of multi-modal communication and, as a result, improve their English language listening and speaking abilities. The experimental results show possibility of the partner robot in the language education; and they also provide considerable insights into developing partner robots that are well suited for immersion in human society.