This study sought to establish the relationship between English Language competency and classroom atmosphere among secondary schools in Arusha District. Through survey design, a sample of 180 students filled the questionnaire. Analysis of data involved Descriptive statistics, T-test and Pearson Correlation. The study established that female students had significantly higher mean score in language competency than male students. Students in classes with 40 or less members had significantly higher mean score than those in classes with more than 40 students. Teachers give necessary support to students for maximized learning outcome and classrooms are clean and orderly, have ideal sitting arrangement and are free from external and internal noise. Language competency is positively influenced by classroom infrastructure and effective teachers' support. The more the teachers give support, the more the learners are motivated to support one another in the process of teaching and learning, thus, likelihood for maximized learning outcome. While teachers need to add more effort to enhance language competency to male students, school administration needs to ensure reduced number of students in classrooms and maintain classroom cleanliness and orderliness for maximized learning outcome.