About 1,500 students applying to the Thomas Jefferson High School for Science and Technology must retake their written entrance exams because of widespread computer glitches Saturday.

The students are semifinalists seeking entry to TJ, as the Northern Virginia magnet school is known. Computer problems at all 15 testing centers caused some students to lose their work or made it impossible for them to submit their essays, which were administered online in an effort to limit adult assistance.

Fairfax County schools officials apologized after about 500 students experienced technical issues with the new online portal. In a letter this week, administrators told parents and students that the test, composed of three short essays and a longer narrative, will be given again.

This time, students will be allowed to write the essays at home between Feb. 6 and Feb. 11. Some parents said their children are upset that they have to take the high-pressure test again, while others questioned if the integrity of the exams can be maintained. On Saturday, the tests were overseen by proctors who ensured that students completed the work on their own. In previous years, the essays were written at home.

“We understand the burden placed on students and parents by having to retake the . . . essay portion of the TJ admission exam,” the school system said in a statement. “Prior to last year, a similar method was used during this portion of the application process and, given the current circumstances, we believe this is the best approach.”

With entry to a prestigious school at stake, parents said there is an expectation that some families might help their children write the essays. Only 480 students are admitted each year. A study commissioned by the school system last year found that there are businesses whose sole focus is helping students gain admission to TJ.

In a letter to TJ officials, Nagendra Kumar Goel and his son, Akhil, an eighth-grader at Longfellow Middle School, wrote that taking the tests at home will hinder the admissions process.

“By allowing students to work at home, they can take input from their families, or take professional advice on what they write,” they wrote. “This is not only cheating, but it doesn’t allow TJ admissions to see how the student thinks and writes, and they instead see the work of many others, flawing the admissions process to many levels.”

Beverly Jurenko, president of the Fairfax County Association for the Gifted, said parents have expressed “a high level of frustration” with the testing problems, adding that her group wants the admissions process to be overhauled.

“Our view is that there are too many essays in the admissions process and that their importance is overemphasized,” Jurenko said. “What we seek is meaningful change in the admissions process that will synchronize the selection of students with the goals and policies” of the school system and the mission of the high school, she added.