This study investigates the use of an assistive humanoid robot for teaching to and learning among young children in an informal learning environment. The robot is called NAO and built by SoftBank Robotics. NAO was used to teach a mathematic concept of measurement to young children. They engaged with the robot through the teaching and learning of presentation slides, worksheets, and playing cards. Their interactions with the robot formed the evidence of their learning. The children also played with the robot in an open and friendly environment, which was video recorded. The efficacy and impacts were measured and analyzed through social signals and verbal responses. Results show that the robot can build a positive and friendly relationship with children while achieving learning outcomes. This study demonstrates the possibilities of introducing NAO into the curriculum and calls for further research toward implementing humanoid robots in classroom settings.