Table 1 Inclusion and exclusion criteria

Inclusion criteria

• Age 3;0 to 6;11 years*

• Attending preschool*

• Exhibiting externalising behaviour problems, that is, either meeting DSM-5 criteria for ADHD on a clinician-rated ADHD checklist (DCL-ADHS) or meeting DSM-5 criteria for ODD on a clinician-rated ODD-checklist (DCL-SSV) plus substantial attention or hyperactivity/impulsivity problems (score ≥ 0.7 on either the inattention or the hyperactivity/impulsivity subscale of the DCL-ADHS)*

• Informed consent of the parents (and, if applicable, the preschool teacher*) and assent of the child

Exclusion criteria

• Intelligence quotient (IQ) < 80

• Comorbidity: pervasive developmental disorder, schizophrenia, bipolar disorder, severe depressive episode**

• Lack of sufficient German-language skills of parents

• Psychotropic medication of the child (except for ADHD medication)*

• Child’s participation in a regular intensive behaviour therapy (on a weekly or fortnightly basis)