In our school district, it is written in the Student Code of Conduct handbook that a cellphone or other electronic device brought to school is subject to seizure if it's used during class. It's also stated that school personnel has the right to monitor any electronic communications by the students anytime, any place, or in any form, including Facebook in the middle of the night or on the weekend.
We had an incident in town where a big feud started brewing between some students on Facebook. Before it escalated into an actual battle, our principal alerted the police who visited the student's homes. We had another incident where a boy was caught with naked pictures of a 12 year-old female student. She sent them to him, and he shared them with about 100 kids on his phone's contact list. It was a BIG DEAL! Every one of those kids had to bring their cellphone and memory card to the principal and vice principal to make the photo was deleted.
So now our district says that for the sake of the community on the whole, it has the right to monitor anything our kids do electronically. The police and parents totally back the district up on this. I agree with it too, and I don't believe a sixth grader has the right to expect privacy over cell phone texts. If one of the kids in the OP were my child, he'd be losing his cell phone for a few months.