Two nationwide sessions of college entrance testing in April and May were canceled Monday as fallout from the coronavirus crisis continued to hammer all aspects of the educational system.

The ACT session scheduled for April 4 was postponed till June 13, and the SAT session scheduled for May 2 was canceled outright. These actions were certain to disrupt the plans of high school juniors throughout the country who are preparing to apply to college.

Most selective colleges and universities require applicants to submit an ACT or SAT score, although there is a growing movement among colleges to make the tests optional.

The College Board, which owns the SAT, said it would issue refunds to those who registered for the May 2 session and to those who had signed up for the March 14 exam but were unable to take it last weekend because of numerous abrupt site closures.

“The safety of students and test center staff is ACT’s top priority,” the nonprofit ACT testing agency said in a statement. “ACT has rescheduled its April 4 national test date to June 13 across the U.S. in response to concerns about the spread of the coronavirus (COVID-19). All students registered for the April 4 test date will receive an email from ACT in the next few days informing them of the postponement and instructions for free rescheduling to June 13 or a future national test date.”

The College Board pointed students to a free test-prep platform called Khan Academy to help them keep their SAT skills sharp while they wait for another chance to take the exam. It promised “as soon as feasible” to provide more testing sessions.

“Together with our member schools and colleges, we will be flexible, thoughtful, and collaborative in exploring ways to continue to support student learning and provide opportunities to test during this challenging time,” the nonprofit organization said in a statement.

It was not immediately clear whether or how other sessions of the two tests will be affected. Monday’s announcements concerned national testing on Saturday mornings. But much of the SAT and ACT testing these days occurs during school days through contracts with states and school systems.

The College Board said it is “working with local partners” and will soon provide updates on weekday SAT testing.

Another pillar of the exam system in potential jeopardy is Advanced Placement testing that occurs in May. With many states shuttering schools in an effort to slow coronavirus infections, students in AP classes have been thrown off their routine at exactly the time when teachers are making the final push to prepare them.

The College Board, which also oversees the AP program, said it is “developing tools to mitigate the impact of school closures.” All AP students and teachers will be able to use free online resources through laptops and mobile phones, the organization said. “These include free online AP lessons and review sessions from some of the top AP teachers in the country,” the College Board said. Some AP students may be allowed to take tests at home.

“We’re working to give every AP student the opportunity to claim the college credit they’ve earned,” the College Board said, promising more details by March 20.