This paper presents a study that aims to address the challenges of creating effective educational robots. To this end, we developed a social educational robot which acts as a peer that is also a learner of a foreign language rather than a tutor teaching it. Children engage in a game with a peer robot which is programmed to either always win or always lose. The purpose of this study is to investigate whether children would learn more if they were winning or losing the game to the robot. The study was conducted with 76 children aged 6-10 years old. The conducted study compares children's responses and children's improvements of English vocabulary after a game with the robot. Results indicate that children improve their English significantly more when playing with the losing robot. In addition, girls rated playing with the robot significantly higher than boys did regardless of the robot's playing strategy.