These six case studies of areas in the world with border disputes could be used as the basis for a class activity where students try to negotiate to settle the dispute. They could use the information provided and conduct additional research to try to figure the best plan for drawing a border.
This is an online quiz asking students to identify the feature that separates the countries. It is a good companion to use, so that students can understand more clearly how some borders are not arbitrary but are ready-made by nature. Students won't know most of the answers but having to look them up will help get the point across.
From the National Geographic online encyclopedia, this information about borders covers the topic and includes a few important examples from Korea to Africa. An excellent explanation, it also includes pictures of examples of some interesting borders around the world.
Your students may be surprised by the sheer number of disputed borders in the world. This interactive map shows all current disputes. You can click on each to get a close up and a little bit of additional information on the dispute.
I love this reference for explaining in clear and simple language what the difference is between a nation and a state. If you can't understand this concept, you will have a difficult time talking about the borders states draw. It's a great place for the teacher to go to for background and for older students as well.
This is an excellent resource, written by National Geographic, that explains everything you and your students need to know about what borders are and how they are or may have been developed for countries. It is a series of 10 lessons. You could use any or all of them to help your students learn about borders. I especially like lesson 1 as an introduction to the idea of borders and the differences between nations and states.