If you have a budget, consider a magazine like Music Alive or InTune. These are produced with adolescents in mind and they connect a variety of genres with music theory and all standards.
Also consider starting them with an inspirational popular song they’ll know (“Beautiful” by Christina Aguilera, “Firework” by Katy Perry) then connecting that to historical composers and whatever else you want to teach them. Most middle schoolers won’t pay much attention unless they think that what is being taught is relevant to their lives. (One of my grad professors said that all teenagers listen to WIIFM – “What’s In It For Me?”) So start with stuff which they like!
This is one of my personal struggles. I’ve always gone straight to the hard core music teaching, but I’ve learned that older students need relevancy first and technicalities later. Band teachers in my building have historically struggled to get students to focus on learning to read notes. A new band teacher has taught the kids arrangements of current pop songs. They’re reading music – some hard rhythm patterns and huge ranges for their age – to be able to play pop songs. (Radioactive, off the top of my head. Soloists at our concert played Let it Go and Counting Stars.) His program is growing and kids are happy. Whatever works, right? 🙂
Have your students make an a capella arrangement of a pop song (it’s legal so long as you don’t publish and sell it!). Add auxiliary instruments (wood block, guiro, shakers, etc) and body percussion (tap knees, stomp, clap, snap, beat boxing). You can print current songs off musicnotes.com for about $5 each.