Minnesota students continue to shine on the ACT college entrance exam, according to results being reported Wednesday.

For a ninth consecutive year, the state's seniors posted the highest average composite score among students in states in which at least half of the graduates took the test.

That average mark — 22.9 out of a possible 36 — was down slightly from the 23.0 posted in 2013. But this year's graduates also finished atop another national measure: the percentage of students deemed college-ready in each of the four subject areas tested.

This year, 39 percent of state graduates tested as proficient across the board on the ACT exam. That result was identical to 2013 and 5 percentage points higher than the 34 percent of students who achieved across-the-board success in second-ranked Wisconsin, the results show.

"I congratulate Minnesota students, teachers and administrators on this tremendous accomplishment," Gov. Mark Dayton said in a statement. "These nation-leading scores demonstrate to the entire country the academic ability of Minnesota students, the dedication of our teachers and the world-class quality of our education system."

Complicating matters, however, at least as it relates to state-by-state comparisons, is the fact that not every senior in every state takes the test.

In Minnesota, for example, 76 percent of graduates, or 45,305 students, were tested in 2013-14, up from 74 percent a year ago. But 12 states, including Michigan, Illinois and Tennessee, now require all seniors to take the ACT, meaning their composite scores reflect the performance of non-college-bound students, too. In Wisconsin, 73 percent of graduates took the ACT exam, and posted an average composite score of 22.2.

Minnesota, which soon will begin requiring all juniors to take the test, has seen considerable success at the individual level. Earlier this year, a Star Tribune survey found that more than 20 seniors and juniors who were still in school had aced the ACT. The number of so-called "36'ers" then grew in subsequent testing rounds.

But the state also is seeing a stubborn gap between white and minority test takers.

According to the results to be released Wednesday, 62 percent of the state's white students reached the minimum college-readiness benchmarks in at least three of the four subjects tested, up from 61 percent in 2013. Black students who met the same standard also rose slightly, from 16 percent in 2013 to 17 percent this year, with the gap between them and white students remaining unchanged at 45 percent.

Gaps widened between white and Asian, Hispanic and American Indian students.

With the exception of Asian students, each of the state's student subgroups outperformed their national counterparts.

For the ACT, students are tested in the areas of English, math, reading and science. Students are deemed college-ready in a given area if they reach the minimum score needed to indicate a 50 percent chance of earning at least a B and a 75 percent chance of obtaining at least a C in a college class.

In Minnesota, 77 percent of students tested hit the college-readiness benchmark for English, followed by 61 percent for math, 56 percent for reading and 53 percent for science. In Wisconsin, the corresponding figures were: 75 percent for English, 54 percent for math, 51 percent for reading and 49 percent for science.

In 2014-15, all Minnesota juniors will begin taking the ACT, free of charge, under new graduation requirements approved by the 2013 Legislature. State officials say the move should help steer more students to post-secondary opportunities and also aid in determining whether students are college and career ready.

"Having all high school students take the ACT will help them understand how well they are prepared for a post-secondary education that fits their needs and interests," said Larry Pogemiller, commissioner of the state Office of Higher Education.

Anthony Lonetree • 651-925-5036