Standards for Severely Disabled Students

Last Monday, as part of Music in Special Education, I had to teach a four mentally retarded and severely disabled students at West Windsor Plainsboro High School North. I brought a song to teach the students, which I found in a fifth grade Silver Burdette book. After about thirty minutes of teaching the song, my students could barely sing it on their own. This caused me to question my expectations of the students. These students are severely disabled. However, should I lower my standards and not expect them to be able to sing the song? Maybe I shouldn’t have been teaching them the song at all. How do I assess students that are severely disabled? What should my standards be?