In this article, we investigate how grammatical competence is manifested in young students’ written texts and how this contributes to the students’ overall writing competence. We pose the following two research questions: (i) Which grammatical features appear in a selection of young students’ texts? and (ii) What do these features reveal about different aspects of the students’ grammatical writing competence? The empirical fundament for this study is a representative sample of texts gathered through the project FUS—Functional Writing in the First School Years. Our primary material amounts to a total of 534 texts written by first- and second-grade students (ages 6–7). The students have completed two writing tasks, in which they were asked to write one descriptive and one narrative text. In our analyses, we see grammatical writing competence as consisting of several sub-competencies—namely, grammatical repertoire, grammatical complexity, grammatical variation, and grammatical choice. Our analyses show that the grammatical repertoire of beginner students is well-developed. The frequency of specific grammatical features differs between the two writing tasks, underpinning the argument that certain text types trigger certain grammatical choices.