These kinds of concerns prompted me last week to email 20 colleges and universities — small and large, private and public, East Coast and West Coast — to ask about their practices. Then I called admissions officials at 10 schools who agreed to interviews.

Each official told me that it was not routine practice at his or her institution for admissions officers to use Google searches on applicants or to peruse their social media posts. Most said their school received so many applications to review — with essays, recommendations and, often, supplemental portfolios — that staff members wouldn’t be able to do extra research online. A few also felt that online investigations might lead to unfair or inconsistent treatment.

“As students’ use of social media is growing, there’s a whole variety of ways that college admissions officers can use it,” Beth A. Wiser, the director of admissions at the University of Vermont, told me. “We have chosen to not use it as part of the process in making admissions decisions.”

Other admissions officials said they did not formally prohibit the practice. In fact, they said, admissions officers did look at online material about applicants on an ad hoc basis. Sometimes prospective students themselves ask an admissions office to look at blogs or videos they have posted; on other occasions, an admissions official might look up an obscure award or event mentioned by an applicant, for purposes of elucidation.

“Last year, we watched some animation videos and we followed media stories about an applicant who was involved in a political cause,” says Will Hummel, an admissions officer at Pomona College in Claremont, Calif. But those were rare instances, he says, and the supplemental material didn’t significantly affect the students’ admissions prospects.

Admissions officials also said they had occasionally rejected applicants, or revoked their acceptances, because of online materials. Often, these officials said, a college may learn about a potential problem from an outside source, such as a high school counselor or a graduate, prompting it to look into the matter.

Last year, an undergraduate at Pitzer College in Claremont, Calif., who had befriended a prospective student on Facebook, notified the admissions office because he noticed that the applicant had posted offensive comments about one of his high school teachers.