Virginia students taking the annual Standards of Learning exams were unable to log in to the tests for more than an hour Wednesday afternoon, the third time in a week that computer problems have disrupted the statewide standardized testing.

Pearson, which administers testing in states across the country, said it is trying to determine what caused the issue.

“As soon as we became aware of the disruption, our teams acted quickly to minimize its impact and return services to normal,” spokeswoman Laura Howe said in a statement. “Our goal is to ensure that students have a smooth testing experience, and we understand the frustration issues like this cause.”

Virginia renewed its contract with Pearson, the world’s largest education company, in July at a cost of $37 million annually for three years. Pearson administers tests nationwide, including the Common Core PARCC exam and others.

Charles Pyle, spokesman for the state Department of Education, said it is not clear how many students were affected by Wednesday’s problems, which prevented students from logging in from 12:20 p.m. to about 1:50 p.m. That meant that students who were scheduled to take tests during that time had to wait more than an hour to begin. Students who logged out in the middle of an exam were unable to complete the test.

Pearson said the company was the target of a cyberattack on May 13 that caused problems with the testing system. On May 14, a computer server became overloaded, leading to further disruptions. As a result of both incidents, 374 students across the state will have to retake exams.

Wednesday’s issue occurred as about 151,000 students statewide took exams. Pyle said that the department still is gathering information from school districts, but it has tallied only 31 students who would have to retake the tests.

Virginia is reexamining its standardized testing and in recent years has moved to reduce the number of tests, which far exceed federal requirements.