In Flanders, there are neither Flemish assessments nor teacher surveys to provide insights into the current practice and outcomes of writing instruction. In the present study, we provide a-state-of-the-art study of the practice of writing instruction in Flemish late elementary education by investigating: (a) how writing is taught, (b) how teachers think about writing and writing instruction, and (c) how student characteristics, teacher characteristics, and classroom writing practices correlate with students' writing performance. In total, 128 teachers and 800 fifth- and sixth-grade students completed teacher and student questionnaires. Students also completed two writing tests (i.e., writing an informational and a narrative text). The descriptive results on the teacher questionnaire showed that upper elementary school teachers spent only about 65 min each week on various writing assignments in class (e.g., stories and worksheets). During these lessons, teachers primarily focused on explicit instruction of writing skills. In addition, teachers were generally positive towards writing and writing instruction and they felt self-efficacious in teaching writing. As to the relationships with students' writing performance, multilevel analyses indicated that students with a high self-efficacy for ideation and autonomous motivation wrote qualitatively better narrative and informational texts, while students with controlled motivation were significantly less successful in writing narrative texts. Also, teacher efficacy for writing was positively correlated with students' informational text quality. In conclusion, this study represents an important starting point in unraveling the black box of writing instruction in Flanders. However, more research is needed to further investigate correlates on student, teacher, and class levels.