It will take time and money to address the problems uncovered by a recent study of on-time graduation rates, the Suffolk School Board said on Thursday.

About three in 10 students who enter ninth grade in one of Suffolk’s public high schools fails to graduate on time, the new state study concluded. The city numbers also fell behind state averages.

“We have some work to do,” School Superintendent Milton R. Liverman said. The Suffolk Public Schools on-time graduation rate was 71.9, nearly 10 percentage points below the state average of 81.3.

The Virginia On-Time Graduation Rate is a new calculation of the number of students who graduate high school within four years of entering the ninth grade.

This is the first year the state has reported the rate, because it is the first time individual students have been tracked over time. The rate is calculated by taking the number of students in the 2004-2005 freshman class, adding transfers in and subtracting transfers out and students who die. The resulting number is then divided by the number of students who earned a diploma in 2008.

Students who earn a GED or certificate of completion are not counted as graduates for the purposes of the statistics.

The on-time graduation rate also is calculated by subgroups – female, male, black, Hispanic, white, Asian, American Indian, other ethnic groups, students with disabilities, students identified as disadvantaged, students with limited English proficiency and homeless students.

Division-wide, the two subgroups that struggled the most were students with disabilities and disadvantaged students – those who qualify for free or reduced lunch. Disabled students had a rate of 58.2, while 59.4 percent of disadvantaged students graduated in four years.

“With these subgroups, it takes more resources and it takes more time,” Liverman said.

Assistant Superintendent Kevin Alston praised the fact that the difference between the black and white students’ rates was less than 6 percent. White, Asian and Hispanic students scored above the division’s average, while black, American Indian and students reporting other ethnicities came in below.

Homeless students – only 13 of them were in the group – had a rate of 76.9, well above the division-wide average. Females graduated on time at a much higher rate than males, 76.4 percent compared to 67.8.

Alston pointed to several programs the schools are already using to help at-risk students graduate on time. They include mentoring of at-risk students by teachers and other staff, remediation, ninth-grade transition and alternative programs for students with behavioral problems.

Other solutions mentioned included finding a way to get credit for graduates from the Pruden Center and finding better ways to track students who transfer out of state.

“We accept it as a challenge,” Liverman said.