Standardized tests continue to pose challenges for students at Pennsylvania's cyber charter schools.

The state Department of Education released test results Thursday that show students at many of the 13 cyber charters operating in 2015-16 were performing far below grade level in both language arts and math.

At 12 of the online charter schools, fewer than 50 percent of students scored advanced or proficient - the benchmark for grade-level performance.

PSSAs are given each year to students in all taxpayer-funded schools in grades three to eight. High school students take Keystone Exams.

At schools where students receive online instruction in their homes, 21st Century Cyber Charter School in Downingtown had the highest scores.

Fifty-seven percent of students scored advanced or proficient in language arts on the PSSA tests; 24 percent did in math.

21st Century, which has about 1,000 students, was founded in 2001 by the intermediate units of the four suburban counties surrounding Philadelphia, and district superintendents serve on its board.

"We are extremely proud of our students and the instruction provided by our teachers here at 21st Century," Kim McCully, CEO of the school, said Thursday.

"The collaboration between school leadership and our school board of superintendents, IU directors, and parents is a key component in our continued success," she said, adding that staffers were thrilled that their students were succeeding.

"We will continue to strive towards remaining the highest performing cyber charter school in the state and will push towards yearly improvement of our scores," McCully said.

Many cyber charters' results were far worse.

At Aspira Bilingual Cyber Charter School in Philadelphia, only 9 percent of students scored on grade level in language arts. None met that benchmark in math.

A total of 96 percent of Aspira students scored below basic in math on the PSSAs - the lowest of the four categories. The rest scored slightly better at the basic level.

Aspira Bilingual Cyber is one of several charter schools operated by Aspira of Pennsylvania, a nonprofit that focuses on Latino youth. Officials could not be reached for comment.

Many cyber educators and parents say that test scores are a misleading measure and that online schools often attract students who have failed in other educational settings.

An Inquirer analysis of PSSA scores found that among area schools, two cyber charters posted some of the biggest improvements over 2015 scores.

At Esperanza Cyber Charter in Philadelphia, the percentage of students scoring proficient or advanced in language arts rose from 8 percent to 24 percent - a gain of 16 percentage points.

The number of students scoring on grade level in language arts at Achievement House Cyber Charter School in Exton improved from 8 percent to 23 percent.

A total of 35,250 students in Pennsylvania were enrolled in cyber charters in the last academic year.

None of the 13 cyber charters met the state's academic benchmark on the performance profiles last year.

The Department of Education said Thursday new school performance profiles - which are based on test scores and other factors - are scheduled to be released next month. 215-854-2789 @marwooda

Staff writer Dylan Purcell contributed to this article.