This quasi-experimental study examined an eighteen-month professional development project focused on improving instructional practices for emerging bilingual and multilingual English learners (ELs). The study is grounded in sociocultural and interactive learning theories related to teaching ELs. Professional development activities included seven graduate-level courses, practical field experiences in schools, instructional coaching from peers and a qualified instructional coach, video demonstrations and observations, and participation in a one-day conference. The research team conducted pre and post classroom observations for 23 in-service teachers and corroborated findings with participant reflections about instructional practices using the Sheltered Instruction Observation Protocol (SIOP). Results reveal that participants made statistically significant increases in seven of the eight areas of instruction: lesson preparation, building background, strategies, interaction, practice/application, lesson delivery, and review/assessment, and no significant change in the area of comprehensible input. The control group showed no significant increases. The discussion identifies strong areas of improvement, moderate areas of improvement, and discusses the one area that showed no significant improvement. Implications for teacher education and professional learning with teachers of ELs are shared along with considerations for future research.