Participants will be randomly assigned to receive either methylphenidate or atomoxetine for either 2 or 5 weeks, depending on how soon they respond to the treatment. After the 2- or 5-week period, participants will be crossed-over to receive whichever medication they did not receive in the first part of the study.

Each item on the 18-item measure is scored on a 4-point scale ranging from 0 (no symptoms) to 3 (severe symptoms), yielding a possible total score of 0-27. Higher score indicates higher probability of diagnosis.

The Clinical Global Impression - Severity scale (CGI-S) is a 7-point scale that requires the clinician to rate the severity of the patient's illness at the time of assessment, relative to the clinician's past experience with patients who have the same diagnosis. Considering total clinical experience, a patient is assessed on severity of mental illness at the time of rating 1, normal, not at all ill; 2, borderline mentally ill; 3, mildly ill; 4, moderately ill; 5, markedly ill; 6, severely ill; or 7, extremely ill.

Measure of social skills, higher score is better. This scale is based on t-scores and does not have psychometrics available.

Measure of conflict within the home over the past 24 hours. The CCI is a validated measure of family conflicts in the home and is completed by parents. It consists of 42 items (for boys) or 36 items (for girls) reflecting attention-seeking and conflictual behavior, as well as negativity and withdrawal. Items are scored as yes (1 point) or no (0 points). Mean score between 0 and 1 reported, with higher score indicating greater conflict.

CPT Commissions, impulsive responses, higher score is worse. This scale is based on t-scores and does not have psychometrics available.

Children's Sleep Problems Severity, sum of scores, higher is worse.The scale assessed contains 16 items, each scored 0 to 3, with 0 representing no problems and 3 representing daily problems. total range from 0 to 48. This score does not have psychometrics available.

Affective problems. This scale consists of 8 items, scored 0-3, with 0 representing no problems and 3 representing extreme problems. This analysis presents sum of scores, higher is worse. Full range from 0 to 24. This score does not have psychometrics available.

Modified Yale Global Tic Severity Scale, sum, higher is worse. This score does not have psychometrics available. The Yale Global Tic Severity Scale (YGTSS) is a semistructured clinician-rated instrument that assesses the severity and frequency of motor and phonic tics over the previous week. Five index scores are obtained during the assessment, where higher scores indicate greater frequency or severity. These indices are: Total Motor Tic Score (0-25), Total Phonic Tic Score (0-25), Total Tic Score (0-50) Overall Impairment Rating (0-50).

Modified Yale Global Tic Severity Scale, sum, higher is worse. This score does not have psychometrics available. The Yale Global Tic Severity Scale (YGTSS) is a semistructured clinician-rated instrument that assesses the severity and frequency of motor and phonic tics over the previous week. Five index scores are obtained during the assessment, where higher scores indicate greater frequency or severity. These indices are: Total Motor Tic Score (0-25), Total Phonic Tic Score (0-25), Total Tic Score (0-50) Overall Impairment Rating (0-50).

Modified Yale Global Tic Severity Scale, sum, higher is worse. This score does not have psychometrics available. The Yale Global Tic Severity Scale (YGTSS) is a semistructured clinician-rated instrument that assesses the severity and frequency of motor and phonic tics over the previous week. Five index scores are obtained during the assessment, where higher scores indicate greater frequency or severity. These indices are: Total Motor Tic Score (0-25), Total Phonic Tic Score (0-25), Total Tic Score (0-50) Overall Impairment Rating (0-50).

Systolic blood pressure - the amount of pressure in arteries during contraction of the heart muscle Normal range varies by age, sex, height and weight and can range from 80mm Hg to 130mmHg

Diastole blood pressure - blood pressure when the heart muscle is between beats. normal range varies by age, sex, height and weight and can range from 34mm Hg to 90mmHg

Heartbeats per minute. Range varies from 50-205 depending on age and level of activity.

Measure of socioeconomic status, score calculated from averaging likert responses, lower = worse

Standardized measure of ADHD symptoms and severity, norm referenced T scores, higher = worse

Standardized measure of ADHD symptoms and severity, norm referenced T scores, higher = worse

CBCL Total Score, measure of psychosocial problems, higher is worse.

Measure of social skills, higher score is better. This scale is based on t-scores and does not have psychometrics available.

Measure of fluency in performance of simple mathematics, sum, lower = worse

Measure of physical activity

Questionnaire, qualitative

Questionnaire, qualitative designed to collect family history, prenatal environmental influences, and developmental history.

Questionnaire, qualitative assesses symptoms of rebound (moodiness, irritability, aggression, and ADHD symptoms) when the medication wears off at night.

Total of all reporting groups

Attention deficit/hyperactivity disorder - hyperactivity/impulsivity (ADHD- H/I). Each item on the 18-item measure is scored on a 4-point scale ranging from 0 (no symptoms) to 3 (severe symptoms), yielding a possible total score of 0-27. Higher score indicates higher probability of diagnosis.

see participant flow section for participants that did not complete blocks

Each item on the 18-item measure is scored on a 4-point scale ranging from 0 (no symptoms) to 3 (severe symptoms), yielding a possible total score of 0-27. Higher score indicates higher probability of diagnosis.

see participant flow section for participants that did not complete blocks

The Clinical Global Impression - Severity scale (CGI-S) is a 7-point scale that requires the clinician to rate the severity of the patient's illness at the time of assessment, relative to the clinician's past experience with patients who have the same diagnosis. Considering total clinical experience, a patient is assessed on severity of mental illness at the time of rating 1, normal, not at all ill; 2, borderline mentally ill; 3, mildly ill; 4, moderately ill; 5, markedly ill; 6, severely ill; or 7, extremely ill.

see participant flow section for participants that did not complete blocks

Measure of social skills, higher score is better. This scale is based on t-scores and does not have psychometrics available.

see participant flow section for participants that did not complete blocks

Measure of conflict within the home over the past 24 hours. The CCI is a validated measure of family conflicts in the home and is completed by parents. It consists of 42 items (for boys) or 36 items (for girls) reflecting attention-seeking and conflictual behavior, as well as negativity and withdrawal. Items are scored as yes (1 point) or no (0 points). Mean score between 0 and 1 reported, with higher score indicating greater conflict.

see participant flow section for participants that did not complete blocks

CPT Commissions, impulsive responses, higher score is worse. This scale is based on t-scores and does not have psychometrics available.

see participant flow section for participants that did not complete blocks

Children's Sleep Problems Severity, sum of scores, higher is worse.The scale assessed contains 16 items, each scored 0 to 3, with 0 representing no problems and 3 representing daily problems. total range from 0 to 48. This score does not have psychometrics available.

see participant flow section for participants that did not complete blocks

Affective problems. This scale consists of 8 items, scored 0-3, with 0 representing no problems and 3 representing extreme problems. This analysis presents sum of scores, higher is worse. Full range from 0 to 24. This score does not have psychometrics available.

see participant flow section for participants that did not complete blocks

Modified Yale Global Tic Severity Scale, sum, higher is worse. This score does not have psychometrics available. The Yale Global Tic Severity Scale (YGTSS) is a semistructured clinician-rated instrument that assesses the severity and frequency of motor and phonic tics over the previous week. Five index scores are obtained during the assessment, where higher scores indicate greater frequency or severity. These indices are: Total Motor Tic Score (0-25), Total Phonic Tic Score (0-25), Total Tic Score (0-50) Overall Impairment Rating (0-50).

see participant flow section for participants that did not complete blocks

Modified Yale Global Tic Severity Scale, sum, higher is worse. This score does not have psychometrics available. The Yale Global Tic Severity Scale (YGTSS) is a semistructured clinician-rated instrument that assesses the severity and frequency of motor and phonic tics over the previous week. Five index scores are obtained during the assessment, where higher scores indicate greater frequency or severity. These indices are: Total Motor Tic Score (0-25), Total Phonic Tic Score (0-25), Total Tic Score (0-50) Overall Impairment Rating (0-50).

see participant flow section for participants that did not complete blocks

Modified Yale Global Tic Severity Scale, sum, higher is worse. This score does not have psychometrics available. The Yale Global Tic Severity Scale (YGTSS) is a semistructured clinician-rated instrument that assesses the severity and frequency of motor and phonic tics over the previous week. Five index scores are obtained during the assessment, where higher scores indicate greater frequency or severity. These indices are: Total Motor Tic Score (0-25), Total Phonic Tic Score (0-25), Total Tic Score (0-50) Overall Impairment Rating (0-50).

see participant flow section for participants that did not complete blocks

Systolic blood pressure - the amount of pressure in arteries during contraction of the heart muscle Normal range varies by age, sex, height and weight and can range from 80mm Hg to 130mmHg

see participant flow section for participants that did not complete blocks

Diastole blood pressure - blood pressure when the heart muscle is between beats. normal range varies by age, sex, height and weight and can range from 34mm Hg to 90mmHg

see participant flow section for participants that did not complete blocks

Heartbeats per minute. Range varies from 50-205 depending on age and level of activity.

see participant flow section for participants that did not complete blocks

Measure of socioeconomic status, score calculated from averaging likert responses, lower = worse

data not collected

Standardized measure of ADHD symptoms and severity, norm referenced T scores, higher = worse

data not collected

Standardized measure of ADHD symptoms and severity, norm referenced T scores, higher = worse

data not collected

CBCL Total Score, measure of psychosocial problems, higher is worse.

data not collected

Measure of social skills, higher score is better. This scale is based on t-scores and does not have psychometrics available.

data not collected

Measure of fluency in performance of simple mathematics, sum, lower = worse

data not collected

Measure of physical activity

data not collected

Questionnaire, qualitative

data not collected

Questionnaire, qualitative designed to collect family history, prenatal environmental influences, and developmental history.

data not collected

Questionnaire, qualitative assesses symptoms of rebound (moodiness, irritability, aggression, and ADHD symptoms) when the medication wears off at night.

data not collected

Block 1 first four weeks received Methylphenidate

Block 2 (weeks 8 to 13) received Atomoxetine

Block 2 (weeks 8 to 13) received Methylphenidate