The high school class of 2006 posted the biggest score increase on the ACT college entrance exam in 20 years and recorded the highest scores of any class since 1991.

Average composite scores on the exam, which measures students’ readiness for college-level work, rose to 21.1 from 20.9 last year. Both boys and girls posted gains, as did all racial groups except Hispanics, whose scores held steady. ACT scores range from 1 to 36.

In Kansas, where about 23,000 students took the test, the average composite score increased to 21.8 from 21.7 last year.

Officials at the independent, nonprofit ACT said an increase of 0.2 points is significant when considered across a record 1.2 million test-takers nationwide, or 40 percent of graduating seniors.

“It takes an enormous amount of change for that large a group to move even a little bit, particularly when that group is changing and we’re seeing more students take the ACT for the first time,” said Richard Ferguson, CEO of the Iowa City, Iowa-based organization.

Some of the improvement may come from the ACT’s growing popularity among high-achieving students in states where the rival SAT exam traditionally has been more popular. The ACT is more attractive to some students because it focuses more on material covered in high school classes than on general ability.

In Connecticut, 12 percent of 2006 graduates took the ACT, up from 10 percent a year ago, and scores rose from 22.8 to 23.1. In New Jersey, 8 percent took the test, up from 6 percent of 2005 graduates, and scores rose from 21.3 to 21.8.

But Ferguson said the national increases were broad-based. Illinois and Colorado – the two states where nearly all 11th graders are required to take the test – saw scores rise 0.2 and 0.1, respectively. Other states with large numbers of ACT takers, such as Kentucky and Tennessee, also recorded increases in line with the national gains.

Historically, the ACT has been more popular in states in the center of the country while the SAT predominates on the East and West coasts. But in addition to Connecticut and New Jersey, Florida, Delaware, Vermont and New Hampshire all had double-digit percentage increases in the number of students taking the ACT.

Next year, Michigan will join Illinois and Colorado in administering the test statewide to 11th graders, and Kentucky will follow in 2008.

In Kansas, the highest average score was in reading, at 22.3, compared with 22.1 last year. The average math score was 21.5, up from 21.4 last year, and the average English score was 21.3, up from 21.2 in 2005. The average science score remained at 21.6.

ACT officials said the national numbers were encouraging but still show that too few students are prepared for college-level work. Only 21 percent of test-takers scored the benchmark indicating they are likely to succeed in college on each of the four exams – math, English, reading and science. More than two-thirds hit the benchmark score in English, but barely one-quarter did in science.

“This doesn’t mean they won’t be successful and graduate from college, but it does increase the likelihood they will struggle or need remediation along the way,” Ferguson said.

Students persuaded to take a full core curriculum – including four years of English and three years each of math, science and social studies – do better on the ACT and are more likely to succeed in college. But the percentage who reported taking the core – which is more than many states require to graduate – actually fell from 56 percent to 54 percent this year.

“The message still isn’t getting across to far too many students,” Ferguson said.

The average score for boys rose 0.1 percent to 21.2, while girls’ scores rose 0.1 to 21.0.

Average scores for black students rose 0.1 points to 17.1, while Hispanics’ scores were steady at 18.6. Significant racial gaps persist: Whites scored 22.0 on average and Asian-Americans 22.3.