Differentiated instruction is an inclusive approach that recognises and values diversities among students and adapts instruction to include every student. The concept of differentiation has been discussed over the past two decades. However, only limited attention has been paid to how pre-service teachers understand this phenomenon, while very little is known about how their beliefs about knowledge and knowing influence this understanding. This study investigated pre-service teachers' understanding of differentiated instruction through the lens of epistemic cognition. The findings suggest pre-service teachers demonstrate a predominantly narrow understanding of differentiation, interpreting it as an instructional strategy of adapting teaching to support struggling learners. In addition, the findings also reveal that diversity is generally interpreted as referring to 'others' and inclusion is considered as a strategy to bring the 'other' people into the mainstream.