My question: Assuming that we need "the language of the language" in order to
speak about language, how do we convey the working terminology without
teaching explicit grammar at some basal point?
 
To me the embodiment of teaching explicit grammar is sentence diagramming.
This seems to be a procedure whereby the means are more complicated than the
ends and where the process--drawing the broken lines here, diagonal lines
there--becomes more tedious than the product. As we know, the transfer of
knowledge from diagram to sentence-writing is lacking. Is this because we lack
the teaching skills necessary to make that leap, or is it because the process
itself is so bogged down with instructions that it falls of its own weight.
 
What's the thinking about diagramming? Can someone explain whether it's worth
the considerable trouble? How does the grammar teacher use sentence
diagramming as the handmaiden of thought?