Differential performance results occur when a specific population subgroup achieves a passing rate which is significantly lower than that of the normative reference group. African Americans do less well, in general, on all types of assessments, including constructed-response tests. The present study examined the writing styles of African American test takers in a National Board for Professional Teaching Standards (NBPTS) portfolio entry from the Middle Childhood/Generalist Certificate, as compared with the writing styles of European American test takers. The use of features other than Edited American English was examined as a possible source of construct-irrelevant variance in assessors' scoring judgments. Thirty-two written commentaries, 18 from African American candidates and 14 from European American candidates, were coded for grammatical, lexical, and discourse features. The coding frame identified features of African American Language (AAL) and Speech Code Errors (SCE). Instances of AAL were fewer than instances of SCE and clustered according to potential users of AAL.