No. If school officials release students to attend an event not sponsored by school or related to school, officials cannot censor the speech of students attending the off-campus event. [1]

[1] Frederick v. Morse, 439 F.3d 1114 (9th Cir. 2006)(finding student banner with drug references, shown at Olympic Torch parade outside high school at a time when students had been released to watch, to be speech protected by the First Amendment; reversing 10-day suspension imposed because principal thought the banner was a positive drug message undercutting the school’s antidrug mission).