Nowadays, differentiated instruction (DI) has become a widely discussed topic in many schools and educational institutes. However, whilst the notion of DI is not new, studies on the effectiveness of DI with respect to student outcomes remain relatively unclear. This may be due partly to the operationalization of DI as well as the narrow focus of many studies on academic performance, thus neglecting other pertinent student outcomes. To address this, the current study aims to examine the impact of a specific DI strategy, namely differentiating according to readiness level and student interest, on intrinsic motivation and perceived competence. Two classes of Primary Six (Year 6 equivalent) students participated in the study, of which one class was pre-classified as high readiness, whilst the other class was pre-classified as low readiness. The research design followed a quasi-experimental single group pre-post-test design and took place in English language classes over a period of five lessons. Results indicated that there was an increase in the level of students' intrinsic motivation and perceived competence in both classes. However, there were no differences in the impact between students with high and low readiness levels. This study demonstrates the effectiveness of a specific DI strategy on intrinsic motivation and perceived competence.