When easy and difficult items are mixed together, their reading aloud latencies become more homogeneous relative to their presentation in unmixed (“pure”) conditions (Lupker, Brown, & Colombo, 1997). We report two experiments designed to investigate the nature of the mechanism that underlies this list composition, or blocking, effect. In Experiment 1, we replicated Lupker et al.'s (1997) blocking effect in the reading aloud task and extended these findings to the visual lexical decision task. In Experiment 2, we found that blocking effects generalized across tasks: The characteristics of stimuli in a visual lexical decision task influenced reading aloud latencies, and vice versa, when visual lexical decision and reading aloud trials were presented alternately in the same experiment. We discuss implications of these results within time-criterion (Lupker et al., 1997) and strength-of-processing (Kello & Plaut, 2000, 2003) theories of strategic processing in reading.