Objective: To examine the validity of sluggish cognitive tempo (SCT) and ADHD–inattention (ADHD-IN) symptoms in children from Chile. Method: Mothers and teachers rated SCT, ADHD-IN, ADHD–hyperactivity/impulsivity (ADHD-HI), oppositional defiant disorder (ODD), anxiety, depression, academic impairment, social impairment, and peer rejection (teachers only) in 652 Chilean children (55% boys) aged 6 to 14 years. Results: For both mother and teacher ratings, the eight SCT symptoms and nine ADHD-IN symptoms showed substantial loadings on their respective factors (convergent validity) along with loadings close to zero on the alternative factor (discriminant validity). ADHD-IN showed a uniquely stronger relationship than SCT with ADHD-HI and ODD whereas SCT showed a uniquely stronger relationship than ADHD-IN with anxiety and depression. Although ADHD-IN uniquely predicted academic impairment and social difficulties, SCT did not. Conclusion: This study provides the first evidence for the validity of SCT among children outside of North America or Western Europe.