I'm sure it varies tremendously by teacher. We had one elementary teacher who basically emphasized shouting as singing. The concerts were loud, but ...
The last two or three years we've had a teacher who is much more atuned to tone. The concerts are much more interesting and the kids seem to learn more about what their voices can do.
One theory I've heard is that it tends to depend on whether the teacher's musical training/education focused on instruments or voice. Those with voice backgrounds are more likely to emphasize the range of opportunities that are available for singing.
For folk, we've benefited greatly by having a teacher who is an active musician himself. He's not a music teacher in the school (media/library, instead), but he's offered and developed lots of music-oriented programs over the 7 years we've been in the school. Everything ranging from having the kids sing Old Dan Tucker to bringing in blue-grass bands to playing himself with parents at school events. When you get someone that active, it tends to spill over to other teachers, too.
For instance, another teacher is using three folkish-type songs in a concert next month (Dan Tucker, Tid-eo, and something that slips my mind just now but I know its in G) and has arranged to have one parent play fiddle, one parent bang on a guitar, and someone else play bass, while she adds the piano. The songs are simple two and three chord music (which is a good thing for some of the musicians, this one, anyway), but they give the kids a chance to sing stuff they wouldn't otherwise and for the kids and parents to hear wonderful instruments like fiddles and basses.