This study examined the hierarchical structure among second/foreign language (L2) writing subskills using a Hierarchical Diagnostic Classification Model (HDCM). A pool of 500 essays composed by English as a Foreign Language (EFL) students was assessed by four experienced EFL teachers using the Empirically-derived Descriptor-based Diagnostic (EDD) checklist. Based on a literature review and the expertise of three content experts, several models were developed to reflect various hierarchical interactions among L2 writing subskills, including linear, divergent, convergent, independent, unstructured, mixed, and higher-order. The comparison of the models showed the presence of an unstructured interaction among L2 writing subskills, indicating that content is the foundational subskill for the mastery of vocabulary, grammar, organization, and mechanics. Higher mastery classes were also associated with higher educational levels, greater frequency of English use, and longer exposure to L2. Understanding the hierarchical relationships among L2 writing subskills can improve targeted instructional strategies and assessment practices. • A constrained version of existing DCMs is represented by hierarchical DCMs. • Models were developed to show hierarchical interactions among L2 writing subskills. • An unstructured interaction among L2 writing subskills was identified. • Higher mastery classes were associated with higher educational levels. • The classes were associated with greater English use and longer L2 exposure.

The present study used the Mixed Rasch Model (MRM) to identify multiple profiles in L2 students’ writing with regard to several linguistic features, including content, organization, grammar, vocabulary, and mechanics. To this end, a pool of 500 essays written by English as a foreign language (EFL) students were rated by four experienced EFL teachers using the Empirically-derived Descriptor-based Diagnostic (EDD) checklist. The ratings were subjected to MRM analysis. Two distinct profiles of L2 writers emerged from the sample analyzed including: (a) Sentence-Oriented and (b) Paragraph-Oriented L2 Writers. Sentence-Oriented L2 Writers tend to focus more on linguistic features, such as grammar, vocabulary, and mechanics, at the sentence level and try to utilize these subskills to generate a written text. However, Paragraph-Oriented Writers are inclined to move beyond the boundaries of a sentence and attend to the structure of a whole paragraph using higher-order features such as content and organization subskills. The two profiles were further examined to capture their unique features. Finally, the theoretical and pedagogical implications of the identification of L2 writing profiles and suggestions for further research are discussed.