The present work aims at investigating the written production of students at a state school in Rio de Janeiro, in order to verify the degree of literacy in Portuguese as a first language of the students as they enroll in secondary school and when they are about to complete it. This Applied Linguistics research, emphasizes the social relevance of the use of language (Moita Lopes, 2006), adopting a textual approach to writing (Hyland, 2002) and following theoretical and methodological assumptions of Systemic-Functional Linguistics, which views language as a system of meanings and functions in both situational and cultural contexts. Focusing on the study of the use of grammatical metaphor (Halliday, 1994) in school texts, through the use of nominalizations, this research proposes the following questions: 1) Do students in secondary school employ the grammatical metaphor in their texts produced in the classroom? 2) Does the use of a more grammatically metaphorical language increase during the cycle of high school? 3) Does the use of nominalizations help to improve the students’ literacy? The set of texts analyzed in this study consists of a social questionnaire, answered by 40 (forty) students in two classes, one of the first year and the other of the third year, so that we could understand who the socio-historically constructed subjects that compound these classrooms are. Exercises that aim at transforming verbal structures into nominal were done by students of the first and third years of secondary school, and analyzed to observe the control of grammatical metaphor through the use of nominalizations. Essays written by these students (N = 50) were also analyzed with the purpose of verifying the use of grammatical metaphor while writing the texts in the classroom. Research results indicate that students have a greater control of grammatical metaphor when they achieve the third year of secondary school. However, they do not use a more grammatically metaphorical language to write their texts in the classroom, showing certain difficulty of using largely grammatical transformations in writing.