The integration of education and robotics has emerged as a crucial development in the technological landscape. This study focuses on the use of a robot teaching assistant to enhance the learning efficiency of 8th-grade students in hands-on STEM activities centered around the theme of "Smart City." It explores the impact of educational robots on students' learning outcomes and their development of hands-on skills through diverse learning methods. Conducted over 12 weeks with 103 participants, the study employed a quasi-experimental design. Students were split into two groups: The Experimental Group (EG), using the 6E model with robot teaching assistants, and the Control Group (CG), using only the 6E model. The analysis of covariance revealed that the EG exhibited superior performance in STEM knowledge, motivation, and hands-on skills compared to the CG. Further analysis indicated that learning motivation significantly influenced hands-on performance in the EG, particularly in high-scoring subgroups. The findings suggest that combining the 6E model with educational robots effectively enhances STEM learning and student engagement. Educational robots as teaching assistants not only aid in knowledge acquisition but also significantly boost students' motivation and hands-on skill development. This implies a promising direction for integrating advanced technology in educational practices to foster more effective learning environments.