In the present article two different L3 learning contexts are distinguished: formal instruction (FI) and study abroad (SA). We analyze the effect of a formal instruction learning context (FI) on students of English as a foreign language. The main objective is to study the impact of FI on the students' lexico-grammatical development. A study was carried out with 36 subjects (advanced L3 English university students) in order to compare their linguistic performance at the beginning of their FI period (T1) and after 80 hours of formal instruction (T2) as measured by a cloze and a sentence rephrasing test. L3 learner results were compared to baseline data (T0) (19 NSs of English, exchange university students) on the aforementioned tests. Statistically significant findings were found for L3 learners' linguistic improvement over the FI period. Implications of the study are presented and discussed.