In parallel with the significant and exciting advancements in robot technologies, the use of humanoid robots to support teaching strategies and learning goals has become a popular topic. Different from the traditional instructional or learning tools, humanoid robots can exhibit mobile behaviours and numerous repetitions and are very helpful to the students in developing problem-solving and collaboration abilities. Presently, the roles of humanoid robots in classrooms fall into four main categories: learning materials, learning companions, teaching assistants and communication mediators to support group learning, respectively. With the humanoid appearance, anthropomorphism, interaction, flexibility, repeatability and digital data representation, humanoid robots have great potential to be useful especially in preschool and primary school education. In this paper, limitations and challenges of the use of humanoid robots as teaching assistants are presented in addition to exploring the relationship between humanoid robots and performance in learning.