The acquisition of academic writing poses challenges for students, who are often provided with little guidance. This article aims to analyze student writing in the early years of university education from a longitudinal perspective, focusing on a student practice - the essay - that is ubiquitous in academia, but roughly defined and rarely problematized. We selected a sample of eight students enrolled in social sciences and humanities programs at a Chilean university who participated in a three-year study to analyze the emergence of voice and positioning. Methodologically, we combined a qualitative analysis of the texts, students' perspectives on their discursive uses, and quantifications of linguistic occurrences in search of discursive positioning resources that contribute to the construction of voice in academic writing. The results show that almost all types of metadiscourse studied increase or become more refined over time, but few do so in a statistically significant way. In addition, participants adhered to simplified views about academic writing, which led them to believe that positioning should be avoided. Consequently, tensions emerge between the desire to express their voice and to meet the expectations of essayist prose. The findings point to the value of teaching metadiscourse to develop a metalinguistic mastery of resources and promote greater agency and the expression of voice in academic writing.