Safety monitoring: Children in the DCS and placebo arms will be seen by Drs. Giza or Choe, who are pediatric neurologists, or their nurse practitioner three to four weeks after the initiation of treatment. In addition, the Cogmed coach will probe for side effects on each coaching call. Side effects will be assessed using a structured instrument and open-ended clinician inquiry. While there are scales for rating stimulant-related adverse events, we are not aware of a broadly accepted tool for glutamatergic agonists. Therefore, we will modify the Physical Symptom Checklist developed for the Research Units on Pediatric Psychopharmacology, which includes a range of potential adverse events.