Experimental measures of working memory that minimize rehearsal and maximize attentional control best predict higher-order cognitive abilities. These tasks fundamentally differ from clinically administered span tasks, which do not control strategy use. Participants engaged in concurrent articulation (to limit rehearsal) or concurrent tapping (to limit attentional refreshing) during forward and backward serial recall with each of three distinct stimulus sets: digits, line drawings of common objects, and images of nonsense symbols. The span tasks used common clinical stopping and scoring procedures. Scores were highest for digits and lowest for novel symbols in all combinations of direction and concurrent task. Furthermore, concurrent articulation and concurrent tapping interfered with backward recall to the same degree. Together, these findings indicate that clinically administered immediate serial recall tasks depend on both rehearsal and long-term lexical knowledge making it difficult to use these tasks to separate problems in language ability from problems in attention.