I love gamifying the classroom. It's a great way to engage students and make learning fun. My experiences have been in lower elementary, but I think my strategies can be applied with middle school content. One of my favorite games to use was Jeopardy. I would create games at sites such as http://www.superteachertools.us/jeopardyx/, where you can enter in whatever topic you are teaching. It does take a bit of prep time, but it's worth it when your administrator does a casual walkthrough and all your students are smiling, laughing, and collaborating in high order thinking questions in a digital game format. Since your students are older, you may even do a gradual release and let students create the questions for the game! This will give them ownership and they feel involved in the learning process. Bonus points to students who can create a whole game, teacher previewed, of course.
You can also try using this strategy using colored chips: http://gettingsmart.com/2012/08/11-steps-gamify-your-next-lesson/. The instructions say to use poker chips, but gambling items tend to be frowned upon in classrooms so I would suggest spray painting buttons or bottle caps as the chips. This also encourages communication and teamwork amongst your students. This can be differentiated for your varied learners. Have fun!