RALEIGH - Even as they consider raising the cap on charter schools in North Carolina, state education officials have started a crackdown on existing charters they say are failing students in Wake and Durham counties.

On Thursday, the state Board of Education cited low test scores for a decision not to renew the charter of SPARC Academy in Raleigh and to limit the renewal of Durham's Kestrel Heights School to just three years, instead of the maximum 10-year extension.

"We need to make sure that charter schools are being held accountable," said Melissa Bartlett, co-chairwoman of the State Board of Education committee that reviews charter schools. "We want charter schools to live up to their potential."

Charter schools are publicly funded and are supposed to provide innovative forms of education. They operate independently of the school districts in which they are located.

More than a dozen schools, five in the Triangle, were hoping to have their charters renewed for 10 years by the State Board of Education this week. Two higher-performing Wake County schools succeeded: East Wake Academy and Franklin Academy.

Woods Charter in Chatham County also received a 10-year renewal and will be allowed to add kindergarten students next year.

But the charter for SPARC Academy, which has 134 students in kindergarten through eighth grade, will expire June 30 and was not renewed.

SPARC, which stands for the Summer Program of Academics and Recreation for Children, has been troubled in recent years. A few years ago, the school was meeting some state and federal standards for progress, but it has lacked certified teachers and enrollment and test scores have declined. This past school year, SPARC was officially labeled a low-performing school by the state with only 40.3 percent of students passing state tests.

McLouis Clayton, chairman of the school's board of directors, said it takes time for any school that serves a population of at-risk students to raise test scores. He added the school was working on correcting its issues, including hiring new teachers who have been certified within the past few years.

"We did all the things we were supposed to," Clayton said. "I thought we'd be on probation with a close watch."

Parents and leaders of Durham's Kestrel Heights School, which serves students in grades six through 12, were also disappointed to receive a three-year charter renewal Thursday.

Officials with the state Department of Public Instruction and the State Board of Education committee overseeing charters recommended the shorter term because test scores at Kestrel have declined over the past three years. Most recently, state scores showed 52.1 percent of students were performing at or above grade level.

State officials also are investigating a complaint from a parent who says Kestrel Heights teachers aren't following the individualized education plan for her special-needs son, says Tim Dugan, the school's director.

Dugan says test scores have fallen at the school because the state has rescaled tests to make them harder. He also says most new students come to the school already more than a grade level behind, and it takes time to see progress.

In addition to approving the school only through 2011, the State Board of Education denied for a second year Kestrel Heights' request to add elementary grades to the secondary school, which has an enrollment of 420 students.

The school already has cleared three acres of its 10-acre Research Triangle Park site for an elementary school, and parents are on a waiting list, Dugan said.

"We have unbelievable anticipation," he said. "A lot of children, including my own, are at the area elementary schools and they're hanging out the windows, they're so packed. ... We provide competition in this community."

State education officials said Thursday they're responding to calls from groups such as the Blue Ribbon Charter School Commission to hold charter schools more accountable for their performance.

The Blue Ribbon Commission also urged legislators this week to raise the cap on charter schools. The state has limited the number of charter schools to 100.

(Staff writer Kinea White Epps and researcher Denise J. Jones contributed to this report.)