During noninstructional times or during lunch hour, students have the right to free speech. This free speech includes verbal and written speech. If the student can engage in secular speech, the same student can engage in religious speech. There is no difference between verbal and written speech other than litter. If the student litters, you simply punish the litterbug but you cannot stop student speech during non-class time.
Students can actively evangelize other students.
The only prohibition against student speech during non-class times is that it must not substantially interfere with the ordinary operation of the school. This does not mean that student speech can be stopped simply because someone disagrees. One Supreme Court case allowed students to wear black armbands protesting America's involvement in the Vietnam War. Tremendous controversy erupted. Some of the students and teachers had family members who were in Vietnam at the time and some had lost dear friends and family.