Sidebar: I get these stickers at the Dollar General. They come 180 to a pack, they come on a convenient wheel in a box that helps dispense them, and they're only a dollar... AND they all come with fun and positive sayings on them like "Good Job" and "Wow!" and "You rock!" It's a win, win, win purchase. Go and grab some!
I set up my process like this. I said, "Did your teacher tell you? I bought too many stickers! Just way too many! I bought all of these (and here I pull out some of the stickers on their long strip and the kids gasp) and I just don't know what I'm going to do with them! Wait! I have an idea!" So then I tell them that I'm going to put on the video that we watched and sang along with last time, a Super Simple Songs version of BINGO. They are excited about this video and also about the idea of the stickers. I tell them that I'm going to come around and listen to them as they sing and do the song. I might bend over and put my ear near their mouth just so that I can hear their singing voice, nothing to be nervous about. Then, if they're doing a really great job and using their singing voice I'll put a sticker on their shoulder.
So we tried it out. I put on the video and it gave them direction of what to do as they sang. We had watched and sang along to it once before and we'd also spent a good deal of time learning BINGO and working through a powerpoint lesson using instruments and dealing with beat/rhythm to teach the song. They knew the song as well as they were going to know it at this point. I wasn't worried that their singing would be hindered because they didn't know the content. I knew that I could assess them and their use of singing voice and that wouldn't be confused with content knowledge.
All in all, I only played the video twice, I got through to all the students in the class, I assessed each one, and I got to work one-on-one with the kids who weren't getting it. In hindsight I realized that I could have stopped and done a visual of all the kids who got it the first time and then write that down for a formal assessment. Then all the kids who fell below that and weren't "stuck" the first time through could go down further on the rubric and get their assessment as well. In the end all the kids got stickers, all felt successful, and all got to sing the fun song where they jumped at the end. Everybody won and I got everyone assessed without pain, tears, or frustration! Sticker Attack to the rescue!