I use Patterns of Sound starting with 5th grade and as they graduate out of that around 7th/8th grade I use One Minute Sight Singing, which has a lot of levels. Maybe would be good for the upper grades, not sure about that since I only teach middle school. But Patterns of Sound is almost all in key of c, some in f, and just 4/4, 3/4 and 2/4, but gets harder with which scale tone it starts on. One Minute does many more keys, but starts only on Do for a while.
Hope that helps a little!