This study reports on the construction of a questionnaire to assess ninth-grade students' use of self-regulated strategies for school writing tasks. Exploratory and confirmatory factorial analyses were conducted to validate the factor structure of the instrument. The initial factor analytic stage (n = 296) revealed a 13-factor scale, accounting for 61.35% of the variance. Cross-cultural validation was carried out involving Portuguese and Brazilian students (n = 732). Multi-group analyses of invariance were performed on the two samples. Results support a theoretically driven second-order model assessing 12 self-regulated strategies for writing. Full configural and metric invariance were established, suggesting that the 34-item measure may be robust to assess the model under investigation across cultures. Findings suggest that the instrument can be a valid theory-based assessment tool to help researchers and practitioners examine how students in transition to high school initiate and control their school writing tasks.