The SAT, once the nation’s dominant college admission exam, fell behind the ACT in recent years after its rival locked up huge swaths of the market through contracts to provide testing in public schools and more students in the Washington area and elsewhere realized that top colleges and universities would accept either test.

Now the SAT’s owner, the College Board, has mounted a comeback in its bid to regain supremacy as a new version of the venerable test is about to be rolled out nationwide in March. The competition between the ACT and SAT — two tests of similar length, nearly four hours long (counting essays), but with significant stylistic differences — affects millions of college-bound students who slog through the grueling ritual every year.

This month Illinois and Colorado took steps toward awarding contracts to the College Board to give the SAT to 11th-graders in public schools, at no charge to the students. Michigan will give the SAT to high school juniors statewide in April for the first time, also for free to the students. Previously, the ACT had a virtual lock on testing in all three states through contracts.

“This is significant,” David Coleman, the College Board’s president, said this week. “These are states that for a very long time have been working with an alternative.”

Wider access to markets where the SAT now has a minimal presence would heighten the impact of the revisions to the test that aim to make it more accessible. The new version, debuting on March 5, will eliminate penalties for guessing, make its essay component optional and jettison much of the fancy vocabulary, known as “SAT words,” that led generations of students to prepare for test day with piles of flash cards. It will also return the SAT’s maximum score, now 2400, to the iconic 1600.

“Of course we are disappointed in some of these decisions, both because of the loss of longitudinal data on progress toward college and career readiness and the investments schools and districts have made in a proven assessment system and the associated programs, services and research,” Paul J. Weeks, ACT’s senior vice president for client relations, wrote Thursday in an email.

After the SAT’s last revision, in 2005, which added a required writing assessment, it lost market share. Coleman said it’s possible the College Board could lose some customers for a brief period during the transition to a new version. Some students and parents say they prefer the familiarity of the ACT to the uncertainty of a new SAT.

“There could be an initial drop because of those concerns,” Coleman acknowledged. But he said he is confident that the new test will overcome “whatever jitters” students may feel — “because everything we’ve done to change the SAT makes it much better for kids.”

About 1.9 million students in the class of 2015 took the ACT, compared to 1.7 million who took the SAT. The SAT total includes overseas students.

Scores on both exams have stagnated in recent years, adding to worries about student performance in high schools, even though graduation rates are improving. SAT scores this year sank to the lowest level in a decade.

The SAT, launched in 1926, historically has had a greater presence on the West Coast, in the Northeast and in the Washington region. The ACT, launched in 1959, has long been dominant in the center of the country and much of the South. The ACT surpassed the SAT in usage in 2012.

The ACT bills itself as a measure of achievement in high schools, closely tied to the curriculum. The SAT, originally conceived as an aptitude test, has moved toward a similar position, aiming to measure what students have learned in school.

In Illinois, the Chicago Tribune reported this week that state officials had decided to drop free ACT testing for high school juniors and instead give 11th-graders the SAT under a three-year contract worth $14.3 million. The ACT protested, and the decision is not final.

More than 157,000 Illinois students in the class of 2015 took the ACT, making it the ACT’s largest state in terms of participation. About 5,700 from Illinois took the SAT.

In Colorado, another state where the ACT has led the market, officials announced Wednesday that the state intends to award a major contract for SAT testing to the College Board.

In Michigan, about 120,000 11th-graders are expected to take the SAT in April when the state offers it in public schools for the first time. “Anytime you change from something familiar to something new, it’s going to create anxiety and stress out in the field with educators, students and parents,” said Andrew Middlestead, Michigan’s director of standards and assessment. But he said the transition has been smooth. “So far we think things have been going fairly well,” he said.

The College Board has also announced plans to provide testing in public schools in Connecticut and New Hampshire in the spring and in New York City in the 2016-17 school year. In all, more than 650,000 students are expected this school year to take the SAT during the school day through arrangements with states and school systems. The test has been provided in D.C. public schools since 2013.

Delaware Gov. Jack Markell (D) said a program to pay for statewide SAT testing in schools has benefited many underprivileged students. Once they take the test, he said, students who previously didn’t consider themselves college material often end up applying to college, getting in and enrolling.

“Even though people are getting sick of tests, they are desperate for opportunity,” Markell said. “That’s what this is about. We didn’t want to leave a single student behind.”