Language ability and socioeconomic status (SES) are two variables shown to impact children's vocabulary knowledge, which is a key component for academic success. To investigate the relationship among these variables, an informal assessment of academic vocabulary knowledge was administered to middle and high school students with language impairment who came from different SES backgrounds. The assessment was conducted at three times during one school year. Descriptive and correlational analyses were conducted. Results have clinical implications for vocabulary assessment and instruction with school-age children from various socioeconomic backgrounds.