Science, Technology, Engineering, and Mathematics STEM has become an international focus of paramount significance. Through educational reform, the United Arab Emirates UAE government has stated national strategic measures in the Vision 2021 to raise students' attainment in TIMSS & PISA standardized assessments as well as promotes STEM education. Furthermore, developing STEM talents within Emirati students is one of the main purposes of the Science, Technology, and Innovation STI Policy. Adding art to STEM has a positive impact on students' attitudes, motivations and interests that leads to developing creativity skills. The purpose of this chapter is investigating the factors that affect teaching and assessing students' creativity. A mixed method design is used to answer the research questions. The study was conducted in a private school in the UAE. The participants are science, technology, language art, and mathematics teachers (n=30). The results of the study emphasized that motivation, cognition and metacognition set as factors affecting students' creativity in STEAM classes. A balance between formative and summative assessment should be considered to shift the focus from raising students' attainment in standardized assessment to developing their creativity skills.