Although sluggish cognitive tempo (SCT) is distinct from attention-deficit/hyperactivity disorder inattention (ADHD-IN), few studies have examined whether SCT longitudinally predicts other symptom or impairment dimensions. This study used 4 sources (mothers, fathers, primary teachers, and secondary teachers) and 3 occasions of measurement (first, second, and third grades) with 758 first grade (55 % boys), 718 second grade (54 % boys), and 585 third grade (53 % boys) children from Spain to determine SCT’s and ADHD-IN’s unique longitudinal relationships with psychopathology, academic impairment, and social impairment over the 1- and 2-year intervals (i.e., first to third grade, second to third grade). For 1- and 2-year intervals using both mothers’ and fathers’ ratings, higher levels of SCT uniquely predicted higher levels of anxiety, depression, academic impairment, and social impairment whereas higher levels of ADHD-IN uniquely predicted higher levels of ADHD-HI, ODD, and academic impairment. For 1- and 2-year intervals across different primary and secondary teachers (i.e., first/second and third grade ratings were provided by different teachers), higher scores on ADHD-IN uniquely predicted poorer outcomes across domains whereas higher scores on SCT uniquely predicted lower levels of ADHD-HI and ODD for both intervals in addition to higher levels of depression (for primary teachers only), academic impairment (for 1-year interval only), and peer rejection (2-year interval only for primary teachers). Overall, SCT was significantly associated with important outcomes independent of ADHD-IN over 1- and 2-year intervals and across four different raters. This study provides further evidence for distinguishing between SCT and ADHD-IN in home and school settings.
