Of all of these, the herbicide one struck me as the truly criminal act -- vandalism, damaging of property. So, school officials might very well involve the police, perhaps depending on the school's experience/history with that sort of "prank." (Has it been an issue before?) Also, depending on what the "hateful slur" actually is, the criminal charges could also include a hate crime of some sort. But, again, that would depend on laws local to your story's setting.
Chalk art washes off. TP cleans up. An unapproved story gets a written apology/retraction in the next issue. To me, these all seem more in-house issues and corresponding punishments (what the others have said about senior week and graduation ceremonies).