This chapter examines the effects of CLIL provision on different aspects of written language competence in order to determine which of these areas profit more and which are possibly unaffected by the experience of subject matter teaching in a foreign language. For this purpose we analysed the written work of students who followed either a traditional EFL curriculum or enjoyed additional CLIL provision. The data were obtained in a double case study at two higher technical colleges in Austria where students were asked to complete a free writing task. The bottom line of the analysis shows the CLIL students clearly ahead of their EFL-only peers on the basis of overall scores, but on closer inspection results tell a more complex story: in the area of lexico-grammar the CLIL students show significant advantages throughout, as they do in vocabulary range and orthographic correctness. On the level of discourse competence and textual organization, however, differences are difficult to discern with the general competence level in this area leaving a great deal of room for improvement. Several explanations for these results suggest themselves.