The goal of this study is to provide a new, early treatment approach for preschoolers with ADHD, which could facilitate the EF developing well to achieve better outcome.

ADHD in preschoolers has become established as a valid psychiatric disorder with characterized core deficits of executive function (EF). The EF impairments occurred in preschool period could persist to childhood, adolescent and adulthood, causing extensive and deep damage of individual's academic and career achievement, social function, and peer relationship. Psychostimulants remain a controversial opinion for preschoolers and appear less efficacious and more common side effects. It is very important to explore the effective nonpharmacological intervention targeting the EF deficits and appropriately tailored to young children. Therefore, the investigators conduct this randomized and controlled study to find out the therapeutic efficacy of metacognitive Executive Function Training for Preschool Children with ADHD (MEFP), and follow the subjects to observe whether the therapeutic efficacy would persist. In the mean time, the investigators also observe the factors which can influence the therapeutic efficacy. The goal of this study is to provide a new, early treatment approach for preschoolers with ADHD, which could facilitate the EF developing well to achieve better outcome.

Inclusion Criteria:

1. meet both the criteria of ADHD based on the interview by the DIPA and clinical diagnosis with DSM-5;
2. full-scale IQ estimated by the Wechsler Primary and Preschool Scale of Intelligence (WPPSI) above 80;
3. their parents volunteered to participate in this study.

Exclusion Criteria:

1. child with severe mental disorder or physical disease that might interfere the assessment and intervention, such as Autistic Spectrum Disorder(ASD), schizophrenia, epilepsy, traumatic brain injury, etc.;
2. receive medication intervention for their ADHD symptoms before study;
3. parents with severe mental illness, such as schizophrenia, mood disorder (period of onset), etc..