True.
The First Amendment does not prohibit praying; anyone can pray in school at any time by just closing their eyes and going for it. What numerous rulings and statues have upheld over the years is that a representative of the government (such as a public school coach) cannot promote any one religion over another. The logical conclusion is that he cannot lead others in prayer or deliver sermons or anything, but as long as he was just silently praying to himself, regardless of where, any interference by other government reps would constitute "prohibiting the free exercise thereof."
And, as it turns out ...
... that's exactly what he was doing.
The Supreme Court says that a high school football coach who knelt and prayed on the field after games is protected by the Constitution.
apnews.com
I'm good with this.