In this research note, Catherine Kim presents the findings of the changes in in-service STEM teachers' beliefs about English Learners (ELs) and English to Speakers of Other Languages (ESOL) education gleaned from the teachers' written reflections in the portfolios submitted at the end of their yearlong participation in an ESOL professional development program. The objectives were to discover how STEM teachers made a self-assessment of what they learned from their ESOL professional development experience and to further evaluate whether it contributed to changing their views on ELs and ESOL education.