Education Secretary Betsy DeVos spoke at Harvard University on Thursday evening about school choice and was introduced by an academic dean who issued a warning: Heckle the secretary or anyone else, and you will be escorted out by Harvard security.

DeVos was the keynote speaker at a conference on “The Future of School Choice,” sponsored by Paul Peterson’s Program on Education Policy and Governance at the Kennedy School of Government at Harvard. A Michigan billionaire, DeVos has been a school-choice advocate for decades in that state, where she helped expand charter schools but failed to get a voucher program passed. She has created and run organizations that have lobbied for school choice around the country.

Hundreds of protesters greeted her outside the forum where she spoke, and during her speech, some students stood up and held politically charged signs, including one that said, “Our Students are Not 4 Sale.” At some points during her speech, shouts from outside could be heard but there were not obvious scenes of security hauling anyone out.

DeVos was introduced by Archon Fung, academic dean at the Kennedy School, who talked about the importance of listening to both sides of important issues — even though the agenda for the two-day conference is packed with speakers who support school choice. There appear to be no speakers opposed to the notion that school choice should be an important feature of public education in the United States.

Fung told the audience, which included Harvard students, “I will ask Harvard University police to escort out anyone who insists on preventing others from speaking or hearing.”

The event came at a time when the nation has been roiled in debate over free speech on campus after speakers, many of them conservatives, have been the target of protests that have led some of the speeches to be canceled. DeVos has been one of the most controversial Cabinet members in the Trump administration and has been greeted by protesters at many venues she has visited.

During his introduction, Fung mentioned that 1,900 people had signed a Facebook page opposing DeVos’s appearance, and he said it reflects “large and profound” differences in American society today. He also said history has yet to decide whether school choice is valuable for children or whether it will be seen as a scam fleecing the public.

DeVos says she supports school choice because it is important to give parents choice and that students should not be trapped in what she calls failing public schools. Critics say that school choice programs — especially those that use public money for private and religious school children — are aimed at privatizing the public education system. That, they believe, is DeVos’s ultimate aim, even though she says it isn’t. She has derided the public education system, however, and once called it a “dead end.”

DeVos gave a speech Thursday evening supporting school choice, hitting on themes she speaks about frequently, including that parents should have a wide variety of education choices for their children. Her focus as a lightning rod was clear toward the end of the event when the audience was invited to ask questions.

A student who obviously opposed school choice asked her how much her net worth would rise as a result of her push to increase school choice policies. Her home state has the most charter schools operated by for-profit companies. She responded by saying that she has written a number of checks to advance the cause of school choice, and that has affected her net worth in a negative way.

Answering another student’s question about Michigan, she said charter schools there generally get better test scores than traditional schools. A 2016 report by Politico, however, said:

Despite two decades of charter-school growth, the state’s overall academic progress has failed to keep pace with other states: Michigan ranks near the bottom for fourth- and eighth-grade math and fourth-grade reading on a nationally representative test, nicknamed the “Nation’s Report Card.” Notably, the state’s charter schools scored worse on that test than their traditional public-school counterparts, according to an analysis of federal data.

(Update: More about speech)