Signs outside Sir Francis Drake High School in San Anselmo, Calif., announce the school’s closure on Tuesday. (Ezra Shaw/Getty Images)

(Update on April 3: More states close schools for academic year)

A growing number of states say their schools will stay closed for the rest of the 2019-20 academic year to stem the coronoavirus outbreak.

As of Friday, April 3, there were a dozen states plus the Northern Marianas Islands in the Pacific that had ordered or recommended that all schools stay closed. And with medical experts warning that the coronavirus is still spreading across the country, other states are expected to join them.

Michigan Gov. Gretchen Whitmer (D) signed an executive order late Thursday officially closing schools for the rest of the school year unless social distancing rules are allowed to ease. She had closed schools on March 16, saying they would reopen April 5, but then pushed that back until April 14 as she enacted a statewide stay-at-home order.

Also on Thursday, Indiana’s superintendent of public instruction, Jennifer McCormick announced that schools in that state would not reopen this school year.

Earlier in the week, Georgia Gov. Brian Kemp (R) said he was cancelling the second semester of the year, and California’s education chief said that state’s school districts should plan to keep their campuses closed and provide distance education for all students.

With infectious-disease experts saying that the spread of the disease will become worse, it is likely that many other states also will keep students at home and try to provide distance learning.

These dozen states are now planning to keep schools closed this academic year: Alabama, Arizona, California, Georgia, Indiana, Kansas, Michigan, New Mexico, Nebraska, Oklahoma, Virginia and Vermont.

Tony Thurmond, California’s state superintendent of public instruction, released a statement late Tuesday saying that “it currently appears that our students will not be able to return to school campuses before the end of the school year” because of safety concerns and the continuing need for social distancing.

With the country engaged in an unprecedented shift to distance learning — with much of it online — Thurmond said California schools should prepare to have curriculum delivered to students through distance learning for the rest of the school year.

“From what we know right now, our schools will be closed longer than we originally thought,” he said, “and it will be best if our schools are prepared for that extension, by having their distance learning models prepared to go until the end of the school year.”

California is one of several states that closed school buildings recently without setting dates to reopen; the others are New Jersey, North Carolina and Pennsylvania. Meanwhile, some states that had expected to reopen schools in March have pushed the dates into April and May.

President Trump had recently said he wanted the country to reopen by Easter, which is April 12, but since then he has said he is keeping federal social distancing guidelines in place through April.

Medical experts say that though social distancing has helped — most but not all have “stay-at-home” orders — the danger that the disease will keep spreading for some time is real. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, said Tuesday night on MSNBC that the duration of social distancing will be extended because many people are not following the guidelines.

Meanwhile, the director of the Centers for Disease Control and Prevention, Robert Redfield, told WABE News in Atlanta that up to 25 percent of people who have the virus may show no symptoms, which can allow it to spread in places that relax their requirement of social isolation.

Some districts are considering ways to help students make up for lost learning, including opening summer school and starting the fall semester early.