A Study on the Pathway of Enhancing Learners’ Academic Writing Syntactic Complexity through Clause-Level Teaching under the OBE Framework

Abstract

This study, framed by the concept of Outcome-Based Education (OBE), investigates the effects of relative clause instruction on learners’ academic writing syntactic complexity and its underlying pathways, using a two-group pretest-posttest quasi-experimental design across eight weeks. Participants were 71 English majors from two intact classes, with Class 221 (n = 35) assigned to the experimental group receiving OBE-aligned relative clause instruction, and Class 222 (n = 36) assigned to the control group receiving conventional academic writing instruction at Liuzhou Institute of Technology. Both pre- and post-tests involved academic writing tasks assessed using multidimensional measures of syntactic complexity. Results showed a significant group × time interaction effect on core syntactic complexity indicators. The experimental group showed statistically significant gains in average T-unit length, subordinate clauses per T-unit, and complex noun phrase density from pretest to posttest, with moderate to large effect sizes; the control group showed only small, non-significant increases over the same period. Between-group comparisons at posttest confirmed significantly higher syntactic complexity in the experimental group after controlling for baseline performance. These improvements were particularly concentrated in dimensions closely associated with relative clauses, and the previously prevalent tendency to avoid subordinate structures observed in the pre-test was reduced in the experimental group. Explicit instruction proved especially effective for morphosyntactic categories characterized by clear rules and complex structures, and its positive associations with target structures were observable across the intervention period. In terms of developmental patterns, individual gains were neither uniform nor smooth but rather marked by distinct nonlinearity and internal fluctuations. Notably, increased precision and deeper subordination at the noun phrase level emerged alongside the intervention, suggesting that the observed syntactic changes stem from a combined activation of relative clauses and noun phrase elaboration. We argue that academic discourse complexity is more prominently reflected in complex noun phrases than in subordinate clauses. Overall, OBE in relative clauses yields greater syntactic complexity gains than conventional instruction within a relatively short period, and these improvements follow a structurally coupled pathway driven by co-development of relative clause use and noun phrase elaboration.