The purpose of the current review is to take stock of the past 20 years of CHC COG-ACH relations research. More importantly, the primary goals are to address the limitations in the Flanagan et al. (2006) synthesis via the use of systematic and operationally defined research synthesis procedures and to add greater specificity to their broad stroke findings as a function of: (a) achievement domains (viz., basic reading skills—BRS; reading comprehension—RC; basic math skills—BMS; math reasoning—MR), (b) age-related or developmental moderated findings, and (c) possible “achievement domain—by —age—by—CHC ability” interactions.  Our goal is not necessarily to criticize the Flanagan et al. (2006) review, but more importantly, to build on their review and extend and refine their work via more explicit and systematic methodological review and synthesis procedures.