Ms. Osgood said that in her experience, one person could clog the pipeline in each of the agency’s 12 regional offices, limiting investigators’ ability to respond to other complaints. It often frustrated investigators who prided themselves on being able to resolve complaints promptly, she said.

“In effect, it turned over the decision-making about how the agency would use many of its resources to a single individual, rather than to agency officials and staff charged with the responsibility for implementing the agency’s stated mission,” she said.

According to the Education Department, 41 percent of the 16,720 complaints filed in the 2016 fiscal year came from three people. The next year, of the 12,837 total cases, 23 percent of them did.

The department calls the complainants “frequent fliers.”

Marcie Lipsitt is proud to be one of them.

In the last two years, Ms. Lipsitt, a disability rights advocate in Michigan, has filed more than 2,400 complaints with the office against schools, departments of education, colleges and universities, libraries and other educational institutions across the country that have websites that people who are deaf or blind or who struggle with fine motor skills cannot navigate.

“No one even knew about this issue until I started filing,” Ms. Lipsitt said. “I didn’t want to get anybody in trouble. I just wanted to raise awareness.”

She has secured more than 1,000 agreements with institutions that committed to bringing their websites into compliance with the Rehabilitation Act of 1973, which prohibits discrimination against people with disabilities and requires that electronic and information technologies be accessible to them.