This inquiry centers on a single group of 22 eight years old choolchildren, exposed to English as a foreign language (EFL) instruction in the fall term and to CLIL instruction (Science) in the winter term. It examines class materials' vocabulary and productive lexical knowledge gains. Students appear exposed to a larger number of words and to more abstract and technical vocabulary in the CLIL materials, but they made notable vocabulary learning advance in both contexts. It is also disclosed that learning English through Science is a more demanding experience than acquiring English in the EFL class.