The "Woodock-Johnson V" Symbol Inhibition test is a measure of the inhibiting and updating aspects of executive functioning, developed for administration on the new "Riverside Score"™ digital platform. This paper describes the development of the Symbol Inhibition test, including the test design, norming and validity study data collection, development of the novel scoring model, and the results of the concurrent and clinical validity study analyses. Preliminary findings suggest that the Symbol Inhibition test, while moderately correlated with overall measures of cognitive ability (g), measures a latent trait distinct from the other broad CHC abilities measured in the WJ V.