William E. Pelham Jr., a child psychologist who challenged how his field approached attention deficit hyperactivity disorder in children, arguing for a therapy-based regimen that used drugs like Ritalin and Adderall as an optional supplement, died on Oct. 21 in Miami. He was 75.

His son, William E. Pelham III, who is also a child psychologist, confirmed the death, in a hospital, but did not provide a cause.

Dr. Pelham began his career in the mid-1970s, when the modern understanding of mental health was emerging and psychologists were only just beginning to understand A.D.H.D. — and with it a new generation of medication to treat it.

Through the 1980s and ’90s, doctors and many parents embraced A.D.H.D. drugs like Ritalin and Adderall as miracle medications, though some, including Dr. Pelham, raised concerns about their efficacy and side effects.

Dr. Pelham was not opposed to medication. He recognized that drugs were effective at rapidly addressing the symptoms of A.D.H.D., like fidgeting, impulsiveness and lack of concentration. But in a long string of studies and papers, he argued that for most children, behavioral therapy, combined with parental intervention techniques, should be the first line of attack, followed by low doses of drugs, if necessary.

And yet, as he pointed out repeatedly, the reality was far different: The Centers for Disease Control and Prevention reported in 2016 that while six in 10 children diagnosed with A.D.H.D. were on medication, fewer than half received behavioral therapy.

In one major study, which he published in 2016 along with Susan Murphy, a statistician at the University of Michigan, he demonstrated the importance of treatment sequencing — that behavioral therapy should come first, then medication.

He and Dr. Murphy split a group of 146 children with A.D.H.D., from ages 5 to 12, into two groups. One group received a low dose of generic Ritalin; the other received nothing, but their parents were given instruction in behavioral-modification techniques.

After two months, children from both groups who showed no improvement were arranged into four new groups: The children given generic Ritalin received either more medication or behavioral modification therapy, and the children given behavioral modification therapy received either more intense therapy or a dose of medication.

“We showed that the sequence in which you give treatments makes a big difference in outcomes,” Dr. Pelham told The New York Times. “The children who started with behavioral modification were doing significantly better than those who began with medication by the end, no matter what treatment combination they ended up with.”

Not everyone agreed with Dr. Pelham’s conclusions, many on practical grounds. Medication was easy to administer, they said, and proper behavioral therapy could be time-consuming and expensive and therefore hard to maintain over a long stretch of time, both for parents and children — especially teenagers, who were more likely to resist it.

Dr. Pelham’s influence can perhaps best be seen in the 2019 guidelines for A.D.H.D. diagnosis and treatment issued by the American Academy of Pediatrics, the group’s most recent recommendations. For very young children, it recommends treatment first, with medication as an option; for children 6 to 12, it recommends both simultaneously. But for adolescents, it concludes that behavioral treatment is unproven, and recommends medication only.

Dr. Pelham began his career at Washington State University but spent most of it at the State University of New York at Buffalo. He moved his research program, the Center for Children and Families, to Florida International University, in Miami, in 2010.

At both schools he ran an innovative summer camp for children with A.D.H.D. and associated disorders. The camp, which he created in 1980, served as a space for both therapy and research. It has since been the model for similar programs nationwide and internationally, including in Japan.

“Dr. Pelham was one of the original giants in the field of A.D.H.D. research,” Dr. James McGough, a professor of psychiatry at the University of California, Los Angeles, said in a phone interview.

William Ellerbe Pelham Jr. was born on Jan. 22, 1948, in Atlanta, the son of William and Kitty Copeland (Kay) Pelham. The family moved often for William Sr.’s work, first to Kensington, Md., where he managed a Canada Dry facility, and later to Montgomery, Ala., where he sold securities. His mother was a homemaker and an artist.

William Jr. received a bachelor’s degree in psychology from Dartmouth in 1970. He spent a year teaching special education in Amsterdam, N.Y., northwest of Albany, before enrolling in the doctoral program in psychology at the State University of New York at Stony Brook, on Long Island. He received his Ph.D. in 1976.

In addition to his son, Dr. Pelham is survived by his wife, Maureen (Cullinan) Pelham, whom he married in 1990; his daughter, Caroline Pelham; and his brothers, Gayle and John.

Dr. Pelham insisted on a therapy-first approach in part because it equipped children with the skills they needed to manage what was often a lifelong struggle.

“Our research has found time and time again that behavioral and educational intervention is the best first-line treatment for children with A.D.H.D.,” he said in an interview with the podcast The Academic Minute in 2022. “They, their teachers and parents learn skills and strategies that will help them succeed at home, in school and in their relationships.”