This study explores to what extent syntactic complexity as assessed by four types of complexity measures may vary in written, argumentative texts of L2 learners (A2‐B1) and native writers of Dutch, Italian and Spanish. All texts were assessed by calculating both overall complexity measures and more fine‐grained measures that focus on the type and number of coordinate and subordinate structures, and the use of post‐modifiers within the NP. The results of the study indicate that there is variation in the process of gradual complexification in written L2 production across proficiency levels, across languages, and between L2 and L1. In line with findings from earlier research, this study shows the importance of employing both general and more specific complexity measures for assessing syntactic growth in L2.