Practitioners working closely with second language (L2) writers in the US recognize at least two types of L2 students: international (IL2) and Generation 1.5 (G1.5) students. Some argue that specific differences in each group's writing performance are evident (cf. Harklau, 2003; Reid, 2006); however, investigations into observable and measurable differences have been minimal. Using a Rasch measurement model, this study offers empirical evidence of how these students may differ in their writing performance, specifically with regard to grammatical, rhetorical, cohesive, sociolinguistic, and content control, in addition to essay length. Two separate statistical analyses were conducted: the first examined differences between IL2 and G1.5 students when modeled together as a single group; the second looked at how the groups compared when modeled separately. Results from the whole-group analysis showed the two groups differed only with regard to rhetorical control; the separate-group analysis revealed differences in length and in the difficulty rankings of the scoring components, with content control ranked at opposite extremes for the two groups. In neither analysis did the groups differ with regard to grammatical, cohesive, or sociolinguistic control as defined in this study. Results are interpreted in terms of students' strengths and weaknesses relevant to placement decisions and instruction. (Contains 8 tables and 4 figures.)