Purpose: This study investigates two extensive reading (ER) programmes carried out in a secondary school in Beijing during the COVID-19 pandemic, with the aim of analysing how differentiated instruction (DI) is reflected in the ER implementation and how this forced online learning inform foreign/second language (L2) pedagogy in relation to ER and DI. Design/methodology/approach: Adopting an exploratory case study approach, the study collected data from multiple sources: interview with six students and two teachers; questionnaire survey (N = 74 + 27); teachers' reflective journal; documents related to the two reading programmes. Data collection lasted for a semester (six months). Thematic analysis was used to code and interpret data. Findings: Following the five-category framework for differentiated instruction (Tomlinson, C. A., and T. Moon. 2013. "Assessment and Student Success in a Differentiated Classroom." Alexandria: Association for Supervision & Curriculum Development), this study collects evidence of DI implementation in terms of "content" (three-tiered system of providing reading materials), "process" (personalised reading frequency and quantity), and "product" (diversified forms/platforms of presentation of reading results) of the reading programmes. However, due to the online teaching mode, DI was not fully reflected in aspects of "affect" (inadequate collaborative activities and interaction between students and teacher) and "learning environment" (lack of studying-together atmosphere). Results also indicate a widening gap between higher and lower achieving learners regarding engagement with ER activities due to differences in student autonomy and parental involvement. Originality/value: This study provides some insights into differentiated instruction in ER implementation in the lockdown period, and proposes implications for L2 pedagogical design and innovation with a DI approach to ER.