The positive effects of Content and Language Integrated Learning (CLIL) on the development of students’ foreign language skills may have been overestimated by previous studies, since most studies failed to consider selection and preparation effects appropriately. Therefore, the present study used complete survey data from a 2002–2007 cohort to investigate English skill development of N = 385 German CLIL and N = 5,578 non-CLIL grammar school students from grade seven (M = 12.46, SD = 0.53) to grade eight (M = 14.46, SD = 0.53). Firstly, we found significant selection effects for performance in primary school, sociodemographic variables, and cognitive abilities. Secondly, after propensity score matching, data revealed significant preparation effects of additional second language instruction for the CLIL students. When controlling selection and preparation effects, only a small and non-significant CLIL effect occurred measured by a C-test. We discuss the results with regard to previous inconsistent findings.

以前的研究可能高估了内容和语言综合学习（CLIL）对学生外语技能发展的积极影响，因为大多数研究未能适当考虑选择和准备的效果。因此，本研究使用来自2002-2007年队列的完整调查数据来调查N = 385德语CLIL和N = 5,578非CLIL语法学校学生从七年级（M = 12.46，SD = 0.53）到年级的英语技能发展八（M = 14.46，SD= 0.53）。首先，我们发现在小学成绩，社会人口统计学变量和认知能力方面有显着的选择效应。其次，在倾向得分匹配之后，数据显示了对CLIL学生的额外第二语言教学的显着准备效果。在控制选择和准备效果时，通过C检验只能测量到很小且不显着的CLIL效果。我们讨论与先前不一致的发现有关的结果。