We had a similar problem with cleanliness in the bathroom in my first internship. We came up with a sign in sheet solution, but put a twist on it. The students had to check off the person that used the bathroom before they used the bathroom, and would ask the other student to clean up any mess that they left. This way, the teacher does not have to stop what he or she is doing to monitor the bathroom. The students run it by themselves, and it seemed to work well for us!

In addition to a bathroom log, enforce a self-monitoring type system, where prior to using the bathroom, the student report any inappropriate bathroom conditions prior to using. When it comes to a single restroom, students are quick to call-out gross/wrong conditions.

In my situation, I have realized that students are not always upset when they get in trouble, but they are extremely embarrassed and upset if the class gets in trouble. Usually other students know who this person is. Each time there is writing in the bathroom, (if you can prove it was from your class) I would have my entire class loose recess or any extra time they are given. Maybe this would help! I would not continue to do it, however, if I noticed it still did not resolve the problem. Usually when they realize they are hurting others who are getting mad about it, they will stop!

It might be a good idea to make sure students do not have any belonging with them when they enter the restroom. Some female students may need to bring a purse with them for personal reasons but otherwise, do not allow students to carry thing with them to the restroom.

I would create a system where the students hold each other accountable. Using the log, if there are any drawings present, everyone who used the bathroom before it was reported would either have to clean the mess up together during recess or share any information they have about who is creating the mess. I would make it clear to students that their classmates won't know what they said, that only the misbehaving student will be punished, and that it doesn't make you uncool or bad to call out others, but can instead help them to grow and improve.

I would say rather then punish the entire class, offer a "bounty" or reward of some kind for information on who is doing the drawing. As someone else mentioned earlier, ofttimes the students know who the guilty person is. You can also make an "anonymous" box, and have students submit information on the perpetrator that way so the "spotlight" isn't shining on them, and they don't feel as guilty for "ratting out" a classsmate.