Final answer:
Dr. H most likely discovered that John's mom was acting like a child and not fulfilling the role of a mother through a case study, which involves in-depth investigations of individuals to understand their behaviors and experiences.
Step-by-step explanation:
The research approach that Dr. H most likely used to discover that John's mom was acting like a child and not fulfilling the role of a mother is a case study.
In a case study, researchers conduct in-depth investigations of an individual or a small group of individuals to gain a comprehensive understanding of their behaviors, thoughts, and experiences. This research method allows researchers to gather detailed information and make inferences about the specific case they are studying.
By conducting a case study on John's mom, Dr. H would have spent a significant amount of time observing and interviewing her, which would have provided valuable insights into her behavior and parenting style.