I'm not sure if this is a prank, or just a case of bizarre willfulness. Staples High School in Westport, Connecticut warned a father and daughter not to bring their horse to school. They brought it anyway, so the school has charged them with breach of peace. From nbc30.com:
Police were called Friday morning when a Westport man and his daughter walked a horse onto the campus of Staples High School, police said. School officials became concerned when a large group of students gathered near the horse and reported it, police said.
School officials had previously warned the family not to bring the horse onto school property and became concerned about the safety of students, police said.
Security personnel at Bedford Middle School in Westport told the father and daughter not to enter the campus with the horse but they entered the property and continued to walk to the high school, police said.
It would be a prank to lock a cow or some other animal inside a school building. But in this case it seems like the father and daughter just really wanted to show off their horse. One hundred years ago it would have been quite normal to ride your horse to school.