This study explores the construct of a summarization test task by means of single-group and multigroup structural equation modeling (SEM). It examines the interrelationships between strategy use and performance, drawing on data from 298 Taiwanese undergraduates' summary essays and their self-reported strategy use. Single-group SEM analyses indicated that the task required multiple constructive strategies of comprehension and composition, including planning, evaluating, discourse synthesis, and source use strategies. The planning and evaluating strategies provided administrative control over other strategies used at varying degrees to improve summarization performance. Multigroup SEM analyses showed that the effects of the planning and evaluating strategies on the discourse synthesis and source use strategies appeared to be invariant across the high (n = 127) and low (n = 122) groups. However, the effects of the discourse synthesis and source use strategies on summarization performance varied across groups. The findings offer insight into the nature of summarization tasks and provide useful validity information for the test task. Implications of the findings are discussed in relation to second language writing assessment and pedagogy.