Measuring receptive vocabulary in German students with special educational needs

Vocabulary knowledge is a core component of language competence and a strong predictor of academic achievement. Clinical and educational diagnostics with vocabulary tests require psychometrically sound instruments that can be applied to diverse groups. Students with special educational needs exhibit pronounced cognitive and linguistic impairments that may compromise the validity of standard vocabulary assessments. This study examined the psychometric quality and measurement invariance of vocabulary assessments among N = 884 sixth graders and N = 4,565 ninth graders attending special and mainstream schools in Germany. The results support unidimensional measurement structures in both student groups and grades that allowed generating reliable proficiency scores. Despite some differential item functioning in Grade 6, the resulting test score bias was minimal and confined to the lower ability range. Overall, these findings indicate that receptive vocabulary can be accurately and comparably assessed among students with special educational needs.