Attention deficit hyperactivity disorder (ADHD) is one of the most common neurodevelopmental disorders in children and adolescents. Its core symptoms, including inattention, hyperactivity, and impulsivity, may persist into adulthood and significantly affect academic performance, family functioning, social relationships, daily living skills, and overall quality of life. Currently, the diagnosis of ADHD mainly relies on clinical assessment because no definitive biological markers have been established. Therefore, reliable and valid instruments for evaluating functional impairment have become increasingly important in ADHD assessment and management. Functional impairment assessment tools can systematically evaluate difficulties experienced by children with ADHD in real-world settings and provide valuable information for screening, diagnostic evaluation, treatment planning, and outcome monitoring. However, most existing ADHD rating scales primarily focus on symptom severity, whereas relatively few instruments comprehensively assess functional impairment across multiple domains. This review summarizes the current research status, clinical applications, and future development trends of functional impairment assessment instruments for children and adolescents with ADHD. Four representative scales, including the ADHD functional impairment scale (ADHD-FX), Barkley functional impairment scale (BFIS), impairment rating scale (IRS), and Weiss functional impairment rating scale (WFIRS), are systematically reviewed. Their psychometric properties, target populations, strengths, limitations, and clinical utility are discussed, with particular emphasis on their roles in diagnostic evaluation, treatment goal setting, and therapeutic outcome assessment. This review aims to provide theoretical evidence and practical guidance for improving the clinical assessment framework of ADHD and promoting the development of individualized intervention strategies.