I like to tell my students that in class we are playing catch. I toss out a statement or question, and they throw back a response. The more meaningful exchanges that take place during a class, and by extension over the entire year, the more they will acquire. It's often that simple.
When two people are playing catch, they aren't going to last very long if one of them is lollygagging everytime she catches the ball. This is why I continually stress the importance of prompt responses. As prompt as can be expected.
Who wants to have a conversation with someone who doesn't respect the communicative skill of immediacy? I personally remember this one well. During my Interpersonal Communications 101 course in college, "immediacy" was the skill I was assigned to study and henceforth improve in my own communication. I learned that it did indeed matter to those whom I conversed with. From then on, unless I was legitimately thinking about my response, or admittedly distracted, I always tried to toss the ball back promptly.
To take the analogy further, when two people are playing catch, they have to know where the other is physically located. If not, the ball will likely not reach them. This means that we teachers are going to have a difficult time providing the i+1 our students need if we aren't getting honest feedback.
Say I throw the ball over my students' heads. (For the analogy to hold up in this part, let's say I'm wearing a blindfold. Really, when we are playing catch with 30 students at once, you could say we are wearing a blindfold of sorts.) Are they going to let me know that I overthrew? If not, chances are I'll do it again. And again. They need to let me know that the ball (my L2 utterance) went over their head. How far? To what side? ("¿Qué significa ___?") This vital information allows me to throw them the ball where they are actually at.
If I'm playing catch with Nolan Ryan, I'm going to have to ask him to throw that ball slower ("Despacio"), or it'll hurt. Or, I'll just be putting my glove in front of my face and praying to Pastaman that it doesn't come near me. Now if The Ryan Express throws the ball and it goes into the tall grass somewhere and I can't find it, I'm going to have to ask him to throw another one ("Repita por favor").
Quality interpersonal communication is quite like a good game of catch.