I said to my student, "Whatcha doin?"
He shrugged.
"Do you understand my question?" I asked. He was a fairly advanced student.
He shook his head.
I slowed it down, but I deliberately retained the phonological contractions, because I had an intuition as to the problem, and I was curious. "What cha doin?" I repeated. I was turning it into a lesson.
There was a long pause. Then he asked, "What is 'cha'?" He was perplexed.
Indeed. Here's the thing: he's not a beginning student. If ever there was a sign that the kids need more interaction with native speakers, this was it.