Abstract Background As a complex cognitive task, integrated writing (IW) requires not only different language modalities but also persistent cognitive effort. In practice, varied language modalities are taught together with IW tasks. However, little research has been done to investigate independent and integrated language tasks simultaneously. In addition, the need for cognition (NfC), which plays an important role in cognitive processing, has not been explored in the context of IW. Aims The present study aims to investigate the influence of different language modalities (i.e., reading and writing) on IW performance and how NfC moderates this influence. Sample A total of 246 Secondary Four students from three schools in Hong Kong. Methods Measures of reading, writing, NfC and IW performance were obtained. Structural equation modelling was used to explore the relationships between reading, writing and IW and investigate the role of NfC. Results Positive effects of reading and writing on IW performance were observed, and writing played a mediating role in the relationship between reading and IW at the same time. Although NfC negatively moderated the influence of reading on IW, it had no moderating effect on the influence of writing on IW. Conclusions The teaching of different language modalities enhances IW performance. The negative moderating effect of NfC on the relationship between reading and IW performance implies that differentiated instruction is required due to individual differences in the influence of reading on IW. Regarding pedagogical implication, teachers should integrate the teaching of reading and writing and focus on cultivating students’ cognitive needs to enhance their IW performance.