More than 31,000 children have been affected by shootings during school hours this year in the United States, The Washington Post reported on Wednesday citing its School Shooting tracker.

The report noted that while school shootings remain relatively rare, guns are brought to school nearly every day.

A total of 13 people were killed in school shootings since the start of the year, including a teenage student and teacher killed at Abundant Life Christian School on Monday, said the report, adding that almost 50 others were shot this year but survived.

Altogether 21 states experienced school shootings this year.

Meanwhile, there have been 426 school shootings since the Columbine High massacre of April 20, 1999, in which 12 students and one teacher were killed. Some 215 people, including children and educators, have been killed in school shootings since Columbine, and almost 500 others have been wounded.

Some 86 percent of the weapons used in school shootings originated from the homes of friends, relatives or parents, in cases where the source of the gun could be determined.

"More than half of school shootings in the United States were carried out by children, none of which would be possible if those children didn't have access to firearms," noted the report.