They're talking about school led, open, out loud praying. Like during the morning announcements or at the start of each class. That is obviously forcing non xtian kids to sit and listen to it. Kids whose families are of other religious faiths will have to listen to it.
Will they do Jewish and Muslim prayers too?
How about Satanic prayers?
Forcing kids to be exposed to religious ideas they don't hold is harmful in that it makes them feel like their school is not interested in them or their ideas and beliefs.