Brooks Hamby made headlines last month when he defied his school's ban on references to Christianity in his graduation speech.
But the matter didn't end when he stepped down from the podium - after thanking Jesus despite the school editing any reference to Him out of three previous drafts of the speech.
Hamby's legal representatives at Liberty Institute want an apology from the school and an assurance that future graduation speeches will not be subject to similar censorship.
The response from the attorneys representing the Brawley Union High School District spans a lengthy 10 pages suggests as much and spells out in no uncertain terms that the school was in the right to ban Jesus from the speech.
The attorneys, from the law firm Atkinson, Andelson, Loya, Ruud and Romo, state that it is "well established in the Ninth Circuit and California that a public school salutatorian has no constitutional right to lead a prayer or include sectarian or proselytising content in his/her graduation speech", Fox News reports.
Hamby defied his school by saying in his speech: "May the God of the Bible bless each and every one of you every day in the rest of your lives."
The letter says 18-year-old Hamby was not permitted to use his salutatory speech to "lead his classmates in a sectarian prayer" and that he should have instead used it to be a "representative example of the success of the school's own educational mission".
"The district was legally obligated to ensure prayers and other sectarian, proseltysing content were omitted from Mr Hamby's speech," the attorneys said.
"Censorship of the speech was necessary to avoid an Establishment Clause."
Speaking to Fox News, Hamby is still happy with his decision to thank Jesus in his speech, despite his lawyers feeling that the school may well be considering a lawsuit.
"I just wanted to say a few nice words and allow people to see the good news - which is the Gospel," said Hamby.
"I'm not an attorney, so I can't speak on behalf of the law, but I think it should never be acceptable to silence students who mention the word God or Jesus. I know in my heart that kind of thing is not ok."