As a key attribute of effective writing, coherence remains challenging to teach in language classrooms, with traditional writing instruction frequently overlooking coherence in favor of discrete, rule-based features. This mixed-methods study investigates the effectiveness of explicit coherence instruction on English-as-a-Foreign-Language (EFL) students’ performance on integrated writing tasks. The study employed a controlled experimental design with 64 upper-intermediate-level undergraduate students at a Chinese university, drawing on Hasan’s Cohesive Harmony theory as the theoretical framework. Half of the participants (n = 32) in the experimental group received explicit instruction on coherence with a focus on cohesive chains and cohesive devices in integrated writing, while the control group (n = 32) received standard paraphrasing instruction. Quantitative analysis revealed that the experimental group showed significant improvements in coherence scores and multiple cohesive chain measures. Qualitative discourse analysis of six students’ writing samples from the experimental group demonstrated varying levels of improvement in writing coherence, with high-performing students showing better use of identity chains and pronoun references. The findings revealed that explicit instruction on coherence significantly improved students’ performance in creating coherent integrated writing, particularly through the development of cohesive chains and appropriate use of cohesive devices. This study underscores the pedagogical value of teaching coherence to enhance writing quality and provides concrete strategies for developing more effective teaching approaches for integrated writing tasks in EFL contexts. • The study examined 64 Chinese EFL students using mixed-methods experimental design. • Cohesive Harmony theory served as the framework for assessing writing coherence. • Explicit instruction significantly improved coherence in integrated writing tasks. • High-performing students demonstrated superior identity chain development.