The Valedictorian is set up to make history. All the other speakers are selected by the school and could arguably have been selected because of their religious views. The Valedictorian is not, and his (or her) words are strictly his own, and the judge's ruling violates his 1st Amendment rights.
The Texas Atty General has stated that the federal judge has overstepped his authority. I wonder if the state police and the local sheriff will back that up. Could be a showdown between the federal police and the state police when the feds try to arrest someone...