RALEIGH - North Carolina high school students are dropping out in increasing numbers despite more efforts to keep them in school, prompting frustrated education leaders to call for raising the minimum dropout age from 16 to 18.

A total of 23,550 students dropped out in 2006-07, representing 5.24 percent of the state's high school population, according to a report released Thursday. That is the biggest number in seven years and a 6 percent increase from 2005-06.

Educators couldn't explain why the numbers are getting worse, but said they reinforce the need for the General Assembly to raise the dropout age. More than three-quarters of North Carolina's dropouts were aged 16 to 18, they said.

"The message needs to be sent that the expectation in the 21st century is that you won't drop out when you're 16," said state Schools Superintendent June Atkinson.

Another report Thursday showed that students are also being suspended in larger numbers. Short-term suspensions rose 2.1 percent in 2006-07 over the prior school year. Long-term suspensions were up 2.7 percent.

Legislators and education officials have been paying more attention to the dropout problem since learning last year that more than 30 percent of high school students aren't graduating. A report released in October by the Milton & Rose D. Friedman Foundation said students who drop out of school in a single year cost the state's taxpayers $169 million annually in lost sales tax revenue and higher Medicaid and prison costs.

Two new committees formed by the General Assembly are focusing on the dropout problem, including a 15-member committee of business and education leaders that last month awarded $7 million in dropout prevention grants. Another group, the Joint Legislative Commission on Dropout Prevention and High School Graduation, will evaluate recipients of the grants to see whether expanding their efforts will help reduce the dropout rate.

The results were mixed for Triangle school districts.

The dropout rate went up in Chatham, Johnston and Wake counties.

A total of 1,647 Wake high school students dropped out this past school year, up 210 from the prior year. Just as with the state numbers, black students represented a disproportionately high percentage of the dropouts at 46 percent.

Johnston County has the highest dropout rate in the Triangle. Superintendent Tony Parker said his system has programs to help remedy the situation, including a revamped Evening Academy for students to retake courses that they failed. Now at Smithfield-Selma High School, it has 20 students, including five dropouts.

"It's a better location," Parker said. "It's viewed in more of a positive light."

Parker said he hopes to expand the program to other high schools.

The dropout rate fell in Durham and Orange counties and the Chapel Hill-Carrboro school system. In Durham, however, the number of students suspended increased by more than 19 percent.

Durham school administrators credit several initiatives for the decrease in dropouts, particularly the creation of smaller, nontraditional high schools, said Debbie Pitman, assistant superintendent of student support services.

"One of the things we're hearing from students who are disconnected, or have dropped out, is that the traditional high school is not a setting where they've been successful, and they don't want to return," she said.

The short-term suspension rate rose in Johnston and Orange counties. It stayed the same in Wake and Chapel Hill-Carrboro. The short-term suspension rate fell in Chatham.

Stephanie Knott, spokeswoman for the Chapel Hill-Carrboro City Schools system, said suspension is "kind of a double-edged sword."

The system's highest number of infractions has to do with drug and alcohol possession, she said. Although cracking down on those offenses increases the suspension rate, it also gives student support teams an opportunity to intervene, she said.

Mike Gilbert, spokesman for Orange County Schools, said his district is working on making sure students who are suspended for longer periods enroll in the alternative high school.

"There's a direct link between the two -- suspensions and dropouts -- because a student in trouble as far as discipline problems is typically going to have academic problems," Parker said.

(Staff writers Peggy Lim, Cheryl Johnston Sadgrove and Samiha Khanna contributed to this report.)