Developmental and learning disorders: Pathology review

An 11-year-old boy is brought to the pediatrician by his parents for evaluation of behavior problems. The patient has been frequently interrupting his parents when they are speaking with others. He often forgets to complete tasks assigned to him, such as cleaning up toys or taking out the trash and is easily distracted. His parents state that when they speak to him, he often does not seem to listen. The patient has been performing poorly in school, and his parents are scheduled to meet with the teacher next week. Past medical history is notable for a tonsillectomy at age 9. Height and weight are consistently tracking at the 50th percentile. Physical examination is unremarkable. Which of the following would be most useful in identifying the patient’s underlying condition?