Solfege is not functional in atonal music and it is foolish to try to force the issue. Because rhythm is language-based, many of the obvious differences involve rhythm. This needs to be addressed and preferably in a manner that is nationally acceptable. Perhaps the most serious difficulty in this country is the lack of time for reinforcement of musical ideas. Hungarian Singing Schools not only have an hour a day within the school day, but additional time for special groups.
Many American schools are lucky to have an hour a week for music.
The same kind of proficiency is impossible in this situation. Inevitably, the question of whether or not to use Orff-style instruments arises. You are very rich in this country and so you must use whatever you have. But first the children must learn to sing perfectly. They must not learn to depend on an instrument to tell them what the pitches are.