About one-third of the D.C. charter schools subject to annual performance rankings are high-performing “Tier 1” schools, according to data the D.C. Public Charter School Board released Friday.

More than half of the schools — 54 percent — are in mid-performing Tier 2. And eight schools, or 12 percent of the city’s ranked charters, are low-performing and in Tier 3. Sixty-eight schools were ranked.

The proportion of schools in each category has been virtually unchanged during the past three years of the charter board’s rating system, which aims to give parents and policymakers a way to assess and compare education choices across the city.

“We’re working to be as transparent as possible about what we mean by school quality and how we assess it,” said Darren Woodruff, vice chairman of the charter board, speaking at a news conference Friday.

Tier 1 schools are freed from certain oversight and are eligible for rewards including priority in competitions for surplus city school buildings and a streamlined process for expanding enrollment. Tier 3 schools are subject to greater charter board scrutiny and can become candidates for closure if they don’t improve.

Schools are scored on a 100-point scale, grading their performance on measures including students’ growth and achievement on standardized tests; student attendance; and re-enrollment rate, or the proportion of families who like a school enough to return.

The highest-scoring charter in the city was KIPP DC’s Key Academy, a middle school in Southeast Washington. It is one of 14 schools that have been ranked Tier 1 for all three years the ranking system has existed.

The lowest-scoring charter was Booker T. Washington, a high school in Northwest Washington’s U Street corridor. It was one of only two schools to be ranked Tier 3 twice in a row; the other is Arts and Technology Academy in Northeast.

Six other schools that had been rated low-performing improved enough to move into Tier 2. Five schools that had been Tier 2 bumped up into the top tier. One was D.C. Bilingual, a Columbia Heights elementary school that hosted Friday’s press conference.

“Tier 1 tells us that what we are doing is working,” said spokeswoman Emilia Pablo. “Bilingual education is positive for students.”

Enrollment in Tier 1 schools has been rising as enrollment in lower-performing schools has dropped, according to charter board officials. Officials said the trend is evidence that parents are using the ratings to make decisions about how best to educate their children.

There are more than 100 charter schools in the city, schools that enroll 44 percent of the city’s public school students. Many of the charters were not ranked, some because they are alternative schools or opened new campuses that resulted in significant student population changes. Others, including early childhood and adult education schools, are currently judged using different standards but will be assigned a tier rating beginning next year.