The only way I have ever been successful in teaching the endings of the five declensions is with songs. I have seen a whole class fail a quiz on the third declension, for example, only to pass it with flying colors, having learned the tune, no more than two weeks later.
Yes, this means you have to sing in front of the class. Yes, you will need to become a choir director. Yes, your students will think it is silly. But they will memorize their endings, and that is all that matters. Just own it, and your students will buy into it. Go slowly, only teaching a new song when your students have mastered the previous one and only teaching the declensions your students need to know (for most this will be the first, second, and third).
Here is a link to the playlist on my YouTube channel with the songs for all five declensions: http://www.youtube.com/user/tantaemolis?feature=mhee#p/c/26586D9347230233