Though as a teacher, you can control what happens in your classroom. Here are some suggestions as to policies and procedures that you may wish to implement to minimize meaningless interruptions.
1. Tell students that if you are in class, then they have no reason to visit you if they are in another class. Students will usually understand and scurry away.
2. Outline policies, discuss policies, and enforce policies. Make sure parents and students know what is expected. You can even provide a written list of the policies and procedures and ask the students and parents to sign them in the beginning of the school year.
3. Outline procedures, discuss procedures and make sure that students follow your procedures. If procedures get sloppy, then have the students practice procedures until they get them right.
4. Lock your door and monitor who comes to see you. If it is a parent wanting to know something from you, then tell the parent that you are teaching and ask him or her to email you, phone you or leave a message in the office for you. Otherwise, schedule a time with the parent when it is a more convenient time, like during your planning period. This is also true for a fellow teacher. Generally, all that a teacher has to do is to be professional about the interruption.