This contribution examines the relationship between the attendance of bilingual/CLIL streams, general EFL (English as a foreign language) proficiency, and English grades. Pre-program and at the two-year mark, CLIL students (N = 414) were compared to non-CLIL students in parallel classes at the same school (non-CLIL/PARA; N = 360) and to regular students from schools without CLIL streams (regular/REGEL; N = 179). CLIL students consistently outperformed the two control groups (0.84 < d < 1.18). However, CLIL did not make a significant contribution to the CLIL students’ advantage in general EFL proficiency, as the magnitude of differences was stable over time. When analyzing students’ grades, results reveal that CLIL students in their high-proficiency classes obtained markedly worse grades than students in the control groups at the same proficiency level due to a big-fish-little-pond effect. Along the same vein, students in non-CLIL classes obtain better grades, on average, than regular students as non-CLIL classes are characterized by lower average proficiency levels. These and other results will be critically discussed in the context of existing studies.