I did this song with my second grades: http://www.carlscorner.us.com/Contractions.htm
I had letter cards for each student, and we took turns coming to the front of the room and spelling out our words. (For example, if the contraction was haven't, students with the letters h-a-v-e-n-o-t would line up.) The rest of the class would start singing the song, and the apostrophe would have to come up and get in the right spot and the popped out letter would have to be back in his/her seat by the time we finished the song.
We also watched a contractions video on BrainPOP Jr. and I did some sorts with them (where they had to match the words with the contractions).