It seems to me that the school in question over-corrected. IMO, it's okay for a student to testify to his/her own experience, but proselytizing the audience crosses the line:
IL School District's Revised Policy Will Allow Christian Preaching at Graduation
Last May, conservative Christians were raising a fuss over Sam ----------, a student at West Prairie High School in Illinois, because administrators at his school said his valedictorian speech for graduation was unacceptable since it included explicitly religious messages.
Once version of the draft speech posted online ended with him encouraging the crowd to accept Christ:
Where did Evil, Justice, Love and Forgiveness converge at a moment in history? Can I take you to a hill called Calvary and show you the person of Jesus Christ?
The Cross of Christ shows us our own evil hearts, that we would put an innocent man up to die. Christ came to show us God's justice in dealing with the unfairness of the world. The Cross demonstrates to us the very love of God who died in our place and how we find at the end of the day that without his forgiveness we would never make it.
... The most important thing in your life is to find that intimacy with God. He will guide you, he will hold you, and he will take you through safely in your journey. As you search for goodness, justice, love, and forgiveness, know that only God is big enough to provide that for you.
The school was right to ask him to change the speech to remove those references--and, to his credit, he did--because they had a policy of approving speeches ahead of time. Had ---------- delivered his sermon after administrators read his speech, critics could have rightfully accused the district of promoting religion at a school event.
But because they did the right thing, they didn't hear from church/state separation groups (who had no need to get involved). Instead, they heard from the conservative legal group First Liberty Institute, which said the school went too far in "censoring" this speech.