This study examined systematic professional development (PD) training and its impact on teachers' roles for and attitudes toward English language learners (ELLs). Systematic PD should compensate for theories and pedagogies not obtained during teacher education programs yet needed for content teachers with ELLs. A study was conducted to examine 6th- to 12th-grade content teachers' report on their instructional strategies for ELLs and their perceived attitude and role changes after they had sheltered instruction observation protocol (SIOP) training and guided coaching sessions. Two surveys and one interview were data sources for this mixed methods research design. Grounded theory was an approach adopted for qualitative data analysis, and t-tests and means were used to analyze quantitative data. The results show that most of the participating teachers perceived that they improved their instructional strategies for ELLs and attributed this improvement to SIOP and guided coaching. The results also show that most of the participants considered their roles for ELLs positively and attributed their attitude change toward ELLs and teaching strategies to PD trainings. Yet some participating teachers reported that they were still frustrated with ELLs, mostly due to their English proficiency levels. Implications and future directions are discussed, as are the limitation of this study.