The current study has a twofold purpose: first, to determine the reliability of a tool for assessing orthographic development in Spanish; second, to assess differences in students' performance on the measure across multiple types of primary schools in a large city in Chile. A Spanish developmental spelling inventory that contained words of increasing orthographic difficulty was administered twice to students in first through fifth grades in three types of schools: public, private and partially subsidised. These school types in large part represent varying levels of student socio-economic status because of costs associated with attending them. Results demonstrate that (a) the Spanish spelling inventory is able to reliably measure the development of orthographic knowledge in Spanish, and (b) there is a relationship between school type and student achievement. The authors describe individual cases to highlight the qualitative nature of differential performance for students in greater- or lesser-resourced schools.