A Study to Evaluate the Efficacy and Safety of Dasotraline in Children 6 to 12 Years Old With Attention-Deficit Hyperactivity Disorder (ADHD) in a Simulated Classroom Setting.

Inclusion Criteria:

1. Subject is 6 - 12 years old, inclusive at screening and randomization.

2. Subject weighs ≤ 30 kg at the time of screening.

3. At least one of the subject's parents/legal guardians must give written informedconsent, including privacy authorization, prior to study participation. The subjectwill provide informed assent prior to study participation.

4. Subject meets Diagnostic and Statistical Manual of Mental Disorders Fifth Edition (DSM-5) criteria for a primary diagnosis of ADHD (inattentive, hyperactive, orcombined presentation) at screening established by a comprehensive psychiatricevaluation that reviews DSM-5 criteria and confirmed using the Schedule for AffectiveDisorders and Schizophrenia for School-Age Children-Present and Lifetime version (K-SADS-PL) at screening.

5. Subject is currently either untreated for ADHD or receiving a treatment regimen of astimulant medication prescribed as monotherapy (i.e., methylphenidate, mixedamphetamine salts, lisdexamphetamine, or dextroamphetamine) within the approvedlabeled dose range for ADHD..

6. In the opinion of the investigator, the subject is not treatment refractory.

7. Any subject not receiving ADHD medication at screening must display clinicallysignificant ADHD symptoms, as measured by an ADHD-RS-IV score ≥ 26 at screening andDay -7.

8. For any subject receiving monotherapy stimulant treatment for ADHD, that treatmentmust be well tolerated and clinically effective based on clinical assessment andinformant interview, as well as, review of available medical records. Note: The ADHDRating Scale Version IV - Home Version (modified for investigator administration) (ADHD RS IV HV) will be administered at Screening by the investigator to informclinical evaluation.

9. Subject is male or a non-pregnant, non-lactating female.

10. Subject, if female, must not be pregnant or breastfeeding, and if ≥ 8 years of agemust have a negative serum pregnancy test at screening.

11. Female subjects of childbearing potential and male subjects with female partners ofchildbearing potential must practice true abstinence (consistent with lifestyle) andmust agree to remain abstinent or agree to use an effective and medically acceptableform of birth control, from the time of informed consent/assent to at least 14 daysafter the last dose of the study drug has been taken.

12. Subject must be in general good health (defined as the absence of any clinicallyrelevant abnormalities as determined by the investigator) based on screening physicaland neurological examinations, medical history, and clinical laboratory values (hematology, chemistry, and urinalysis). Note: If any of the hematology, chemistry, orurinalysis results are not within the laboratory's reference range, then the subjectcan be included only if the investigator determines the deviations to be notclinically relevant.

13. Subject is within the 3rd to 97th percentile for gender specific weight-for-age fromthe Centers for Disease Control and Prevention (CDC) growth charts

14. Subject must report a history of being able to swallow capsules.

15. Subject and subject's parent/legal guardian must be able to fully comprehend theinformed consent/assent forms, understand and be willing and able to comply with allstudy procedures and visit schedule, and be able to communicate satisfactorily withthe investigator and study coordinator.

16. Subject, on Day -1, has evidence of clinically significant ADHD symptoms as measuredby an ADHD RS IV HV total score ≥ 26. If subject has been receiving stimulantpharmacotherapy for ADHD the ADHD RS-IV should be administered following a minimum 72hour washout from prior ADHD medication treatment.

Exclusion Criteria:

1. Subject or parent/legal guardian has commitments during the study that would interferewith attending study visits.

2. Subject is currently being treated for ADHD with a non-stimulant product, or has beentreated with a non-stimulant product in the 4 weeks prior to the start of screening.

3. Subject has failed 2 adequate courses (dose and duration) of stimulant ornon-stimulant treatment for ADHD.

4. Subject is considered treatment refractory, as judged by the investigator.

5. Subject currently has a diagnosis of asthma that has required daily treatment withbronchodilators or nebulizer treatments in the 30 days prior to screening and/or whomay require daily treatments with these agents over the course of the trial.Intermittent use of bronchodilators is not exclusionary. Subjects who have a historyof requiring persistent asthma treatment should be discussed with the medical monitorprior to randomization.

6. Subject has any clinically significant unstable medical abnormality, chronic disease,or a history of a clinically significant abnormality of the cardiovascular,gastrointestinal, respiratory, hepatic, or renal systems, or a disorder or history ofa condition (eg, malabsorption, gastrointestinal surgery) that may interfere with drugabsorption, distribution, metabolism, or excretion. Note: Active medical conditionsthat are minor or well-controlled are not exclusionary if they do not affect risk tothe subject or the study results. In cases in which the impact of the condition uponrisk to the subject or study results is unclear, the medical monitor should beconsulted. Any subject with a known cardiovascular disease or condition (even ifcontrolled) must be discussed with the medical monitor during screening.

7. Subject has a history or presence of abnormal ECGs, which in the investigator'sopinion is clinically significant. Screening site ECGs will be centrally over-read,and eligibility will be determined by the investigator based on the results of theover-read report.

8. Subject has any diagnosis of bipolar I or II disorder, major depressive disorder,conduct disorder, obsessive-compulsive disorder, any history of psychosis, autismspectrum disorder, disruptive mood dysregulation disorder (DMDD), intellectualdisability, Tourette's Syndrome, confirmed genetic disorder with cognitive and/orbehavioral disturbances. Note: Subjects with oppositional defiant disorder (ODD) arepermitted to enroll in the study as long as ODD is not the primary focus of treatment.

9. Subject has a first-degree relative (biological parent or sibling) with a history ofschizophrenia, schizoaffective disorder, bipolar I disorder, or bipolar II disorder.

10. Subject has generalized anxiety disorder or panic disorder that has been the primaryfocus of treatment at any time during the 12 months prior to screening or that hasrequired pharmacotherapy any time during the 6 months prior to screening.

11. Subject has evidence of any chronic disease of the central nervous system (CNS) suchas tumors, inflammation, seizure disorder, vascular disorder, potential CNS relateddisorders that might occur in childhood (eg, Duchenne Muscular dystrophy, myastheniagravis, or other neurologic or serious neuromuscular disorders)

12. Subjects with a history of persistent neurological symptoms attributable to serioushead injury.

13. History of febrile seizure, drug-induced seizure, or alcohol withdrawal seizure isexclusionary.

14. Subjects taking anticonvulsants for seizure control currently or within the past 2years are not eligible for study participation.

15. Subject has uncontrolled thyroid disorder as evidenced by thyroid stimulating hormone (TSH) ≤ 0.8 x the lower limit of normal (LLN) or ≥ 1.25 x the upper limit of normal (ULN) for the reference laboratory

16. Subject answers "yes" to "Suicidal Ideation" item 4 (active suicidal ideation withsome intent to act, without specific plan) or item 5 (active suicidal ideation withspecific plan and intent) for any lifetime history on the C-SSRS Children'sLifetime/Recent assessment at screening.

17. Subject has any history of attempted suicide or clinically significant suicidalideation, in the opinion of the investigator.

18. Subject has a history of severe allergies to more than 1 class of medication ormultiple adverse drug reactions or has a history of allergic reaction or has a knownor suspected sensitivity to any substance that is contained in the study drugformulations

19. Subject has history of intolerance (safety) or lack of efficacy to stimulants.

20. Subject has taken any antipsychotic medication within 6 months prior to screening.

21. Subject has taken any herbal and/or complementary treatments, eg, St. John's Wort,within 6 months prior to Day 1.

22. Subject has taken any antidepressant medication (eg, bupropion, selective serotoninreuptake inhibitor [SSRI]/ serotonin norepinephrine reuptake inhibitor [SNRI],tricyclic, etc) within 6 months prior to Day 1.

23. Subject has ever taken any monoamine oxidase [MAO] inhibitor at any time.

24. Subject is currently undergoing ongoing or newly initiated Cognitive BehavioralTherapy (CBT) for the treatment of ADHD; behavioral therapies, including school basedinterventions that were initiated less than one month prior to screening; or,behavioral therapy that in the opinion of the investigator would interfere with thesubject's ability to participate for the duration of the study. School basedinterventions that have been in place for more than one month prior to screening willbe allowed. Note: Unavoidable changes in school-based interventions that occur duringstudy participation will not be exclusionary, but should be documented by theinvestigator, to the extent possible. Subjects should not be enrolled who, in thejudgment of the investigator, are expected to start substantially different or moreintensive course of behavioral therapy over the duration of their participation in thestudy.

25. Subject or subject's family anticipates a move outside the geographic range ofinvestigative site during the study period, or plans extended travel inconsistent withthe recommended visit interval during study duration.

26. Subject has history of, or current, malignancy other than non-melanomatous skincancer.

27. Subject has history of positive test for Hepatitis B surface antigen or Hepatitis Cantibody.

28. Subject is known to have tested positive for human immunodeficiency virus (HIV).

29. Subject has participated in a classroom study within 6 months prior to the start ofscreening or has participated in any other clinical study with an investigationaldrug/product within 90 days prior to the start of screening or is currentlyparticipating in another clinical trial.

30. Subject shows evidence of substance or alcohol use or is currently using tobacco orother nicotine-containing products, or has a positive urine drug screen (UDS) atscreening. Note: Subjects with a positive UDS may be allowed to continue in the study,provided that the investigator determines that the positive test is as a result oftaking medications as prescribed after consultation with the medical monitor.

31. Subject is taking any disallowed medications for chronic treatment.

32. Subject has previously been enrolled in a clinical trial of dasotraline (SEP-225289).

33. Subject's parent/legal guardian is an investigational site staff member or therelative of an investigational site staff member.

34. Subject is, in the opinion of the investigator, unsuitable in any other way toparticipate in this study.

35. Subject's sibling or family member living in the same household is participating inthe same laboratory classroom cohort for this study.

36. Subject is unable to perform at the basic level of the standardized math test asdefined in the laboratory classroom manual.