This chapter presents an analysis of the Dutch and English writing proficiency of students who learned Dutch as a second language, compared to students for whom Dutch is the first language. Participants are 13/14 year-old secondary school students. The point of departure in the analyses is a regression model in which writing proficiency is decomposed into three types of constituent subskills: linguistic knowledge (vocabulary, grammar, and orthographic knowledge), speed or fluency of processing linguistic knowledge (word retrieval and sentence building), and metacognitive knowledge of both text characteristics and reading and writing strategies. This study investigates whether there are structural differences in both the Dutch writing and the English writing of the non-native speakers of Dutch compared to their native Dutch-speaking peers. Our hypothesis is that the two groups will differ in their Dutch writing, but not so much in their English writing. Using structural equation modelling, we firstly test whether the writing model for the native Dutch writers, with respect to the explanatory value of the constituent skills, holds for the non-native Dutch writers as well. Secondly, we test whether the English writing ‘decomposition’ is the same across the two student groups. Despite the differences in writing proficiency, no essential differences between the two groups were found in the pattern of weights of either Dutch or English writing proficiency on the three types of predictor variables (language knowledge, retrieval speed, and metacognitive knowledge).