"Who's going to take the tests? The most prepared," said John Jesse, State Office of Education assessment director. "But the less prepared students are taking it now" without Utah scores going down.
The scores of the nine states with a statistical participation of 100 percent are: Utah 20.7, Illinois 20.6, Colorado 20.4, Michigan 19.9, Wyoming 19.8, Kentucky 19.6, Tennessee 19.5, Louisiana 19.5, North Carolina 18.7.
ACT uses a statistical model to calculate the percentage of students taking the test rather than individual student data from districts and charter schools. Utah's actual participation rate is not 100 percent, explained Judy Park, State Office of Education associate superintendent for student services.
States that did not have a 100 percent participation rate were not included in the comparison.
Nationally, average ACT scores declined from 21.1 in 2012 to 20.9 in 2013. ACT officials said the decline was a result of new standards and more students taking the test, even those not planning on attending college.
The average scores of some Utah minority students increased from last year, including Latinos (17.5 in 2012 to 17.6 in 2013) and blacks (16.9 to 17).
Other groups declined, including Asian students (20.9 in 2012 to 20.7 in 2013), Pacific Islanders (17.2 to 16.8) and American Indians (16.4 to 16.1).
The more high school students are ready for college, the less they need to take remedial courses, which are often not for credit.
ACT officials define a high school student as ready for college or trade school if he or she has the knowledge to succeed without taking a remedial course. Success is defined as the student having at least a 75 percent chance of earning a C grade and a 50 percent chance of earning a B, based on results in each of the four ACT subject areas: English, reading, science and math. They are measured on a scale from 1 to 36 points.
"What this data says to me, is that when you compare Utah's results with states that have comparable participation, Utahns are getting an extraordinary return on their investment in public education," State Superintendent of Public Instruction Martell Menlove said.
The Associated Press contributed to this story.