This paper aims to describe the longitudinal evolution in the use of English L2 connectives made by students enrolled in a bilingual CLIL programme in the Andalusian secondary education system (Southern Spain) over three years of formal instruction. The automated tool Coh-Metrix has been used to approach a learner corpus produced by students as part of the school subject of bilingual history, which is taught in English as an L2. The overall evolution of connectives has been analysed, as well as the evolution of each of the connectives' categories measured by Coh-Metrix (causal, logical, adversative/contrastive, temporal, extended temporal and additive connectives). Results have then been interpreted in order to pinpoint the developmental stage of students' L2 written proficiency and analyse their degree of historical literacy. Over the three years of our study, the students have been found to increase their overall use of connectives in 15%, indicating that they are becoming more proficient L2 writers. Furthermore, there is a particular increase in their use of causal and adversative/contrastive connectives, and a decrease in extended temporal connectives, which points to the development of their historical literacy and their transition from narrative to expository texts.