Task-based language teaching (TBLT) emphasizes the role of pre-task planning (PTP) in improving learners' second language (L2) performance. PTP's impact on L2 writing quality, however, remains debated. Some studies suggest PTP reduces cognitive load and improves writing, while others find no or even negative effects, highlighting the influence of factors like learner preference and task difficulty. The sociocultural perspective emphasizes the potential benefits of collaborative planning. This study addresses the gap in research by exploring the comparative effects of CP, IP, IPCP, and NP on EFL learners' writing quality and investigating the transferability of these effects to a new writing task. This is important because it examines the combined effect of individual and collaborative planning, a previously unexplored area, and also assesses the learning transfer, which is crucial for evaluating the long-term effectiveness of any instructional method.

The literature review examines existing research on pre-task planning in L2 speaking and writing, collaboration in L2 writing, and the comparison between individual and collaborative pre-task planning. Studies on PTP in L2 speaking show generally positive effects on fluency and complexity, with mixed results for accuracy. In L2 writing, findings are more inconsistent, with some studies reporting positive effects on syntactic complexity, while others show no effects or even negative effects on lexical complexity and fluency. Research on collaboration in L2 writing shows mixed results, with some studies reporting improved accuracy in collaborative writing, while others found no significant differences or even negative effects on fluency and complexity. Studies comparing IP and CP have yielded inconsistent findings, with some showing advantages for CP in certain aspects of writing quality, but not others. This inconsistency highlights the need for further investigation into the effects of combining CP and IP, and also for examining the transferability of the effects to new writing tasks. The study aims to address these gaps by comparing the four planning conditions and examining the transfer effect to a new task.

This study employed a between-group quasi-experimental design. 120 Chinese EFL freshmen (B1 proficiency level, based on NCEE scores) were divided into four groups (CP, IP, IPCP, and NP), with each group receiving different task instructions. Two argumentative writing tasks were used. For Task 1, participants in the CP, IP, and IPCP groups received 10 minutes of planning time (5 minutes each for IP and CP in the IPCP group), while the NP group wrote immediately. Task 2, a new writing task without planning time, was administered a week later. Writing quality was assessed using CAF (Complexity, Accuracy, Fluency) measures. Complexity included lexical sophistication (logarithmic word frequency – LFAW), lexical diversity (all words hypergeometric distribution diversity – AW HD-D), and syntactic complexity (mean length of T-units – MLT, dependent clauses per T-unit – DC/T, coordinate phrases per clause – CP/C, and complex nominals per clause – CN/C), all analyzed using specialized software. Accuracy was measured as error ratio, and fluency as total number of words. Inter-rater reliability for error coding was above 0.85.

One-way ANOVAs revealed significant differences among the groups for syntactic complexity measures in both Task 1 and Task 2. For both tasks, the CP group consistently demonstrated significantly higher syntactic complexity (MLT, DC/T, CP/C, and CN/C) than the IP, IPCP, and NP groups. Post-hoc Tukey tests confirmed these differences. No significant differences were found among the groups for lexical complexity (LFAW, AW HD-D), accuracy (error ratio), or fluency (total number of words) in either Task 1 or Task 2.

The findings support the hypothesis that collaborative pre-task planning enhances syntactic complexity in EFL learners' writing. This effect is consistent across both immediate and delayed post-tests, indicating learning transfer. The lack of significant differences in lexical complexity, accuracy, and fluency suggests that CP's benefits may be primarily focused on syntactic development. The results contrast with some previous research, which might be attributed to differences in task complexity, genre, and the structured nature of pre-writing tasks used in other studies. The unstructured nature of the pre-writing task in this study might have encouraged CP groups to focus more on generating ideas, leading to more complex sentence structures. The absence of effects on other CAF measures may be due to factors like individual contributions in CP, group size, and the focus of discussion during the planning phase.

This study demonstrates the positive impact of collaborative pre-task planning on syntactic complexity in EFL learners' writing, with this effect persisting in a subsequent writing task. However, it highlights the limited scope of CP's benefits to specific aspects of writing quality. Future research should investigate the influence of individual differences, explore different planning implementation options, and utilize think-aloud protocols and self-report questionnaires to understand student planning processes and perceptions.

The study's limitations include the lack of investigation into the role of individual differences (motivation, self-efficacy), a focus only on participatory structure in planning, and the lack of exploration into how students used planning time and perceived the learning transfer process. The sample consisted of Chinese EFL learners with intermediate proficiency, limiting the generalizability of findings to other proficiency levels or contexts.