This study aimed to explore the lived experiences of general education classroom teachers (grades 1-5) who have been highly effective in using arts integration and their perceptions of using the arts for formative assessment. The study explored the ways in which teachers with high self-efficacy integrating the arts designed and facilitated arts-based formative assessment as well as teachers' perceptions of student learning when using the arts to formatively assess. This study used a phenomenological approach to gather insights from eight elementary teachers at eight different schools in a large metro public school district. Data were collected through in-depth interviews, classroom observations, and lesson materials. The findings revealed how arts-based formative assessment methods were used to differentiate diverse learners and make student thinking visible. The findings discussed the different ways arts-based formative assessment can be used when designing rubrics and implementing instruction. Findings linked the learning environment, teacher collaboration and professional learning, and teachers' growth mindset to high teacher efficacy with assessing arts integration. When exploring teachers' perceptions of student learning when using the arts to formatively assess, high student engagement, collaboration, and immersion in the creative process were positively associated with social, emotional, and academic growth in students. The study's findings highlighted implications for teachers, school and district leaders, and arts integration training programs. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]