Parents of families who will be randomized in Group PC will first take part in behavioral parent training. After the completion of the parent training program and the assessment (Time 2 assessment), their children will take part in the individualized child training program.

Children of families who will be randomized in Group CP will first take part in the individualized child training program. After the completion of the child training program and the assessment (Time 2 assessment), parents will take part in the behavioral parent training program.

The parent training consists of 8 weekly group sessions where parents are trained on behavior modification techniques, optimal parental practices as well as techniques for the enhancement of their children's cognitive deficits.

ADHD Rating Scale-IV (Greek version, parent report) is a clinician-administered questionnaire completed by the child's parents. The scale consists of 18 questions that assess inattention (9 items) and hyperactivity/impulsivity (9 items). The total score is obtained by adding the raw scores of Inattention subscale and Hyperactivity/impulsivity subscale. Each item is rated on a 4-point Likert scale (0=Never or Rarely, 1=Sometimes, 2=Often, 3=Very Often) with total scores ranging from 0-54, while inattention subscale score and hyperactivity/impulsivity subscale score range from 0-27 each. A higher score indicates more severe ADHD symptoms.

Changes in scores of Inattention subscale, Hyperactivity/Impulsivity subscale and Total Score will be evaluated before, during and after the intervention as well as at a follow-up assessment (3-4 months after the end of the intervention program).

Attention Network Task (ANT child version) is a computerized task that was developed to measure the three networks of attention in children as described by Posner and colleagues, namely the alerting network, the orienting network and the executive control network.

The scores for each network are obtained by reaction time subtractions of different stimulus combinations (cues, congruent conditions, incongruent conditions).

Changes in scores of alerting network, orienting network and executive control network will be evaluated before, during and after the intervention as well as at a follow-up assessment (3-4 months after the end of the intervention program).

Go/No-Go task is a computerized task that was developed to measure attention and response inhibition. The task was developed by the research team in accordance with Conner's CPT-III task and the participant responds to certain stimuli (Go-trials) and withhold response to other stimuli (No-Go trials). There are 6 blocks of 60 trials (80% go-trials, 20% no-go trials) and there are four scores obtained from participants' responses: 1) Correct hits rate, 2) Omission error rate (do not respond in a target, inattention), 3) Commission error rate (response on a no-go trial, impulsivity) and 4) Reaction time of response on a go-trial (slower RT shows inattention).

Changes in: 1) average correct hits rate, 2) average number of omission errors, 3) average number of commission errors and 4) reaction time variability will be evaluated before, during and after the intervention as well as at a follow-up assessment (3-4 months after the end of the intervention program).

Working Memory Index (WISC-V) measures a child's ability to register, maintain and manipulate visual and auditory information in mind. Working Memory Index from WISC-V consists of two subscales: Digit Span and Picture Span.

Changes in Working Memory Index results will be evaluated before, during and after the intervention as well as at a follow-up assessment (3-4 months after the end of the intervention program).