ABSTRACT The aim of the present study is twofold. In the first place, it aims at examining and comparing the written compositions of two groups of undergraduates enrolled in a University Degree in English Studies, using as measures accuracy and grammatical complexity. It also intends to describe the development of the morphological, syntactic, punctuation and spelling errors as English is used by these learners. A total of 100 learners of English as a foreign language participated in the study. They were divided into two groups according to their Oxford Placement Test score: group A was formed by 36 advanced students (C1 as per the Common European Framework of Reference for Languages (CEFR)); and group B was made up of 64 upper intermediate students (B2 as per the CEFR). The analysis of the compositions collected showed significant differences between advanced and upper intermediate students both in complexity and in accuracy. The figures indicated that there was an improvement trend between B2 and C1. However, the differences between groups were significant only in spelling and in punctuation errors. Although the upper intermediate and advanced EFL groups investigated were mainly found to be dominated by progress, there were nevertheless some cases of error stabilization and regression tendencies.