The current study compared the immediate (post-intervention) and long-term (6-months later) effects on reflective judgment (RJ) of an argument mapping-infused Critical Thinking (CT) training course versus CT training using hierarchical outlines (HO) and a no-CT training control condition in students scoring high and low on baseline CT dispositions. While previous studies have demonstrated effects of argument mapping (AM) training on CT outcomes, no AM study to date has focused on RJ outcomes and no study has examined if CT dispositions moderate the effect of AM training on RJ outcomes. AM is a method of diagrammatically representing arguments, designed to simplify the assimilation of an argument structure and facilitate analysis and evaluation of propositions and relations. Eighty-one undergraduate students scoring high and low on CT dispositions were randomly allocated to either an AM-infused CT training group, a HO CT training group or a no-CT training control group and were tested on RJ ability using the Lectical Reflective Judgment Assessment before, immediately after and 6-months after a six-week intervention period. Results revealed a main effect of CT disposition, with higher CT disposition associated with higher RJ scores at all testing times. Students scoring low on CT dispositions, trained through AM, showed a significant increase in RJ performance from pre-to-post-testing. Conversely, students scoring high on CT dispositions, trained through AM, showed a decrease in RJ performance from pre-to-post-testing; whereas both the HO and control groups showed a significant increase in RJ performance from pre-to-post-testing. Findings are discussed in light of research and theory on RJ development and the best practices for CT instruction through AM.