To improve the focus of English Learner (EL), professional development for in-service teachers who may have experienced gaps in prior preparation for serving ELs, this two-part study begins with detailed survey-based data collection and analysis of teachers' perceived preparedness to serve ELs. The data highlights specific priorities for EL-focused professional development grounded in the Teaching English to Speakers of Other Languages (TESOL) P-12 "Professional Teaching Standard" in the domains of language, culture, instruction, assessment, and professionalism. Based on those survey findings, the article shares recommendations for specific content to be included in EL-focused professional development for teachers who reported feeling underprepared to serve ELs. Finally, this study provides specific recommendations for school leaders in relationship to the study.