Leslie Altman Rescorla, 75, a developmental psychologist at Bryn Mawr College whose specialty was language delay in toddlers, died Monday, Oct. 12, of cancer at her home in Havertown.

Dr. Rescorla balanced her life in Bryn Mawr and later, Havertown, with time spent in Colchester, Vt., the home of her husband, Thomas M. Achenbach, a professor of psychological science at the University of Vermont.

Dr. Rescorla was Class of 1897 Professor of Science, an endowed academic chair, from 2010 to the present. She retired in May and then became Class of 1897 Professor Emeritus of Science.

She headed Bryn Mawr College’s psychology department for many years and directed its Child Study Institute, a multidisciplinary clinic that served children and families for 60 years until closing in 2018.

For 35 years, she was director of Phebe Anna Thorne School’s early childhood programs. Thorne is a laboratory preschool and kindergarten at Bryn Mawr College.

“The Thorne school embodies Dr. Rescorla’s research and understanding of young children,” said school director Amanda Ulrich. “She will be greatly missed.”

Dr. Rescorla also pushed for collaboration between the Haverford and Bryn Mawr College psychology departments.

“Leslie was a role model as a teacher, scholar, and citizen of the college community,” said Bryn Mawr president Kim Cassidy. “In the classroom, she modeled passion and enthusiasm for the field, and shared joy in watching students learn. She was an extraordinarily productive scholar whose research on language development had enormous impact across disciplines and around the world.”

Gifted and energetic, Dr. Rescorla rarely stopped moving, said her brother William Altman. “My sister was brilliant and whip-crack smart, and didn’t make other people feel stupid,” he said. “She was an Energizer Bunny of vitality and activity.”

Born in Washington on VJ Day, 1945, her middle name was Victoria. She graduated from Holton-Arms, a preparatory school in Bethesda, Md., and earned a bachelor’s degree from Radcliffe College in 1967, a master’s degree from the London School of Economics, and a Ph.D. from Yale University in 1976.

Dr. Rescorla received her clinical training at Yale Child Study Center, Children’s Hospital of Philadelphia, and the Philadelphia Child Guidance Center. She joined the Bryn Mawr College faculty in 1985.

In addition to delayed language acquisition, her research interests were long-term patterns of academic aptitude and achievement in children; and in collaboration with Achenbach, comparative psychopathology among children, adolescents, and adults from around the world.

Her contribution to science was a vocabulary checklist developed in the 1980s to identify late talkers at age 2. It’s used to help determine whether children have language delay or more serious conditions, such as intellectual disability, hearing impairment, or an autism spectrum disorder.

At a Vancouver conference in March 2012, Dr. Rescorla outlined the minimum 25 words that 2-year-olds should have mastered. They included cookie, milk, and dog, according to the Globe and Mail of Toronto. Further, she said, the normal range for a 2-year-old is 75 to 225 words.

“This and other work is aimed at trying to pinpoint children who can benefit from early intervention, since language delays can have long-lasting negative effects on a child’s education and behavior,” the newspaper wrote.

Dr. Rescorla held out the hope of improvement to parents worried about their children’s slow development, Altman said. “Here’s this brilliant Ph.D. who knows exactly how to talk to them,” her brother said. “She was an amazing blend of fierce problem-solving and intelligence, combined with genuine affection for people.”

She wrote several books, including the 2013 Late Talkers issued by Brookes Publishing Co., and was a sought-after international lecturer, including in Italian.

When not working, she took up ballroom dancing, cross-country skiing, and cooking. On trips abroad, she saw so many of the sights that she wore out her traveling companions, her brother said.

Dr. Rescorla married Robert Rescorla in the early 1970s. They had two sons before divorcing. He is now deceased. She married Achenbach in 2000.

Besides her brother William and husband, she is survived by sons Eric and Michael; four grandchildren; two other brothers; and a sister. Two sisters died earlier.

A memorial service is being planned at Bryn Mawr College for next spring.