Inclusion Criteria:  children, adolescent and young adults (Aged 6-15); have sufficient proficiency in Chinese to understand verbal instructions and give informed consent; clinically significant mild to moderate ADHD syndromes requiring intervention; without learning disabilities and intelligence quotient (IQ) score not lower than 70; are "more likely to commit time in the projects" for reasons such as intention to treat and receiving the New ADHD+ service.  Exclusion Criteria:  known diagnosis of intellectual disability; not reaching syndrome diagnostic threshold for ADHD; already receiving medical interventions / treatments at Hospital Authority (HA) and/or private sector; known psychiatric diagnosis (stabilized diagnosis and treatment); current or active suicidal ideation or attempts; have received structured psychosocial intervention for more than 3 contact hours (for waitlist group); and refusal to give consent.