Bossier Parish Schools has 34 elementary, middle and high schools and one alternative school, the district said.
In a letter sent to parents, Superintendent Scott Smith said, "Freedom is not free. Each day the men and women at Barksdale Air Force Base and in other branches of the military in Bossier Parish and throughout the nation don a uniform and put their lives at risk as they proudly serve and protect us with honor. The least Bossier Schools can do is expect our student athletes to stand in solidarity when the National Anthem is played at sporting events in honor of those sacrifices."
The district provided the letter to CNN. It said players and coaches should stand during the National Anthem "in a show of respect." This also applies to those who join a club or a student organization that requires a faculty sponsor, the letter said.
"It is a choice for students to participate in extracurricular activities, not a right," the letter said.
If students don't comply, the district is leaving the consequences to principals and coaching staff to decide, the letter said.
Smith said the letter was sent "in light of the national conversation currently taking place." But it pins the issue as one intended to show support for the military, without acknowledging why the protests have become so controversial.
Debate over pro athletes protesting during the playing of the National Anthem has raged since last year, when former San Francisco 49ers quarterback Colin Kaepernick began to kneel during "The Star-Spangled Banner" as a way of protesting police brutality and racial inequality in America.
Things intensified a week ago, when President Trump blasted NFL athletes and team owners over such protests, saying the owners should fire any "son of a bitch" player who took a knee during the anthem.
"I guarantee, things will stop," Trump said.
Afterward, more than 200 NFL players protested during the anthem during the weekend's games. Other players and some team owners locked arms during the anthem as a show of unity.