SAN DIEGO -- The Academic Performance Index score for San Diego Unified schools -- summarizing students' performance on a series of tests -- rose by 18 points in 2008-09, above the statewide average.

The district's score went from 749 last year to 767. The statewide API score increased by 14 points, from 741 last year to 755, according to figures released today by the California Department of Education.

The scores range from 200 to 1,000, with a performance target of 800.

"This is wonderful news for the hard-working students, teachers and staff at these elementary schools," outgoing SDUSD Superintendent Terry Grier said. "We've put a particular emphasis on smaller classes, which we know leads to better learning.

"These scores certainly show the growing excellence of our elementary and middle schools, but they also show we have a great deal of work to do," he said. "Our high schools, for example, range from some of the very best in the state to others that face great challenges."

According to the state, 42 percent of California schools met the 800-point bar or exceeded it in 2008-09, compared to 36 percent in 2007-08.

API reflects growth in student achievement from one year to the next. It is determined by results on the California Standards Tests, the California Achievement Tests, 6th Edition tests and California High School Exit Exam.

"For the seventh year in a row, schools at every level have made real progress toward the statewide API target of 800, and almost half of our elementary schools have met or exceeded this goal," said State Superintendent of Public Instruction Jack O'Connell.

"The API results also show a slight narrowing of the achievement gap that historically has left Hispanic or Latino and African-American students trailing behind their peers who are white or Asian," he said. "I am delighted to see this trend of progress continue."

Fifty-one percent of schools statewide also met their federal Adequate Yearly Progress benchmarks -- down slightly from 52 percent last year.

Under the No Child Left Behind federal law, schools must meet annual Adequate Yearly Progress targets, which increase over time, so that in 2013-14, 100 percent of students are expected to score at the proficient level or above.

O'Connell noted that high schools showed a particularly sharp decline in meeting AYP benchmarks, a fact he said could be attributed to the increasing difficulty in high school curriculum.

The Adequate Yearly Progress measures whether a school and all its significant student subgroups met a single benchmark of achievement in a single year.

A school not meeting Adequate Yearly Progress may fall short in every category, or miss the mark narrowly by failing one of many criteria measured.

API growth is one of the elements to determine whether a school makes it over the Adequate Yearly Progress bar.