No studies have analyzed differences between mother, father, and teacher ratings of cognitive disengagement syndrome (CDS; formerly sluggish cognitive tempo). The sample included 1,115 children with autism and/or attention-deficit/hyperactivity disorder (ADHD) 4-16 years of age who were rated by mothers on the Pediatric Behavior Scale. Subsets of these children were also rated by fathers and/or teachers, resulting in 896 mother/father, 964 mother/teacher, and 745 father/teacher dyads. The CDS factor comprised four items assessing the core features of CDS: cognitive disengagement (in a fog/confused and stares/preoccupied/in own world) and hypoactivity (sluggish/slow moving/low energy and drowsy/sleepy/not alert). Overall, 37% of teachers, 22% of mothers, and 16% of fathers rated the children as significantly elevated on CDS symptoms. Teacher scores were significantly higher than mother scores, whose scores exceeded those of fathers. Agreement on whether a child had CDS was fair-moderate for mothers and fathers but poor for parents and teachers. Findings of more severe CDS teacher than parent ratings are in marked contrast to the opposite pattern found in studies of anxiety, depression, ADHD, oppositional behavior, conduct problems, autism, bullying, and victimization. Children may display fewer behavior problems at school than at home, and parents may be more aware of their child's internal state than teachers. However, teachers may be more aware of the cognitive component of CDS that might interfere with functioning in the classroom more so than at home. Cognitive demands in school may reveal and intensify CDS symptoms. Findings highlight the importance of multi-informant ratings in research and clinical practice. (PsycInfo Database Record (c) 2023 APA, all rights reserved).