Executive function (EF) contributes significantly to reading comprehension across the lifespan. Emerging research indicates domain-specific assessments of EF are better suited for assessment and intervention in academic contexts. For example, "graphophonological-semantic cognitive flexibility" (GSF), the ability to flexibly switch between the graphophonological and semantic components of printed words, contributes uniquely to reading comprehension across the lifespan, and GSF training improves children's reading comprehension. This study compared the original GSF measure, which is problematic for use in schools due to its subjectively interpreted explicit explanation component, to an abbreviated implicit task that is better suited for assessment of GSF in practical contexts in 68 first and second grade students. Implicit and explicit GSF contributed uniquely to reading comprehension concurrently and longitudinally when children (n = 31) were in third and fourth grades, beyond verbal ability, decoding ability, and matrix reasoning.