If so, here's a helpful visual aid you can print and post in your classroom. I've made several of these for the most common usage errors I see in my students' writing samples (and on Facebook, Twitter).
You can find this anchor chart (without my blog tag) and many more here: http://www.teacherspayteachers.com/Product/Common-Grammar-Usage-Problem-Areas-Anchor-Charts
I also posted quizzes and activities to compliment the frequently confused words here:
Have a great weekend, everyone! Aren't you glad it's Friday!?