In this study, we analyzed the perceptions of treatment teachers who participated in a randomized controlled trial study which targeted a science-infused literacy intervention, "Let's Talk Science," for first grade English language learner students. Three aspects, including the effectiveness of the intervention, details of instructional practice, and recommendations of teachers, were investigated. We used the qualitative approach of content analysis. Results suggested that (a) the intervention had a positive result for both treatment students and teachers and (b) four core strengths contributed to the successful effect of the intervention related to science-infused literacy -- professional development, time-scripted teaching materials, effective questioning strategies, and visuals and hands-on activities. We advocate that special consideration be given to English language instructors' ongoing professional development, as well as to the learning environment with a lowered affective filter using effective instructional strategies.