This study explored factors associated with English as Second Language (ESL) and English Literacy Development (ELD) students' performance on the Ontario Secondary School Literacy Test (OSSLT) from three aspects: 1) the relationship between test performance and the characteristics of ESL/ELD students; 2) the relationship between ESL/ELD students' aggregated school performance and their school-level socio-economic status; and 3) the comparison of ESL/ELD and non-ESL/ELD students' performance on three test formats in the reading component of the OSSLT. Test data from 4,311 ESL/ELD students and 5,003 non-ESL/ELD students, their responses to the Educational Quality and Accountability Office's (EQAO) Student Questionnaire, and school-level socio-economic status data from the Education Quality and Indicators Program (EQUIP) were analyzed. The results of this study offered insights into identifying and understanding factors that influenced ESL/ELD students' OSSLT performance. The results also provided directions for future research and instructional support in relation to ESL/ ELD students in the context of the accountability framework in Ontario.