How do the kids feel about the piece? And how long have you been teaching it? If it’s been over a month trudging through the piece and the kids are not enjoying it, I’d say choose something simple and new which they can perform well. Their attitude about a piece effects the performance quality and how they appear while performing. If most still like it, stick with it and make your decided changes / cuts. …. Another possible problem if you continue with this song is that the kids who are well behaved may (if they haven’t already) get annoyed at the kids who are misbehaving and create more behavior problems!! Happened to me with a couple classes before.