The study examined impact of exposure to out-of-class English language learning activities on language proficiency in selected secondary school in Lira District, Uganda. It was based on socio- constructivist and input-based theories of second language acquisition.  A convergent mixed-methods research design was adopted utilizing quantitative survey data with qualitative research findings from focus group discussions with students and semi-structured interviews. The data was collected from students and the teachers of English by use of structured questionnaires, interview guides, and focus group discussion protocols. Quantitative data was analyzed using descriptive and inferential statistics and for qualitative data, thematic analysis was involved. The study found that regular engagement in out-of-class English learning activities significantly enhances Students English language proficiency. Specifically, digital media-based activities, online educational content and interactive social media engagement were considered as the strongest indicators of proficiency. Qualitative findings too validated the results indicating that exposure to authentic language environment enhanced learners' vocabulary, their speaking confidence, pronunciation, listening comprehension, and motivation to use English in real-life contexts. However, several barriers were identified to effective out-of-class learning such as:  internet connectivity issues, access to digital gadgets and reading materials, socioeconomic status, limited parental support and predominant use of local languages in students' home environments. The study concluded that out-of-class learning is a useful complement to classroom instruction and contributes significantly to English language proficiency. It suggested that educational institutions, educators, parents and policy makers promote structured out-of-class learning opportunities for learners through technology-enhanced learning, community literacy initiatives and supportive language environments among students in secondary schools.