In many cases, this only indicates your teen is absolutely normal in this regard! It's funny how, as adults, we see our kids as "non-verbal", yet when they are with their peers or on Face book, or texting they are anything but. With my kids, I found that they felt put "on the spot" when talking to adults or before groups....and talking before groups is the #1 fear most people have.

SO my suggestions are:

1. Put this in perspective. Is this really a problem, or is it actually normal behavior? Of course, if it goes beyond normal, professional counseling could do wonders!

2. How is your child's confidence in general? A confident person who has things in the back of their mind to talk about (current events, popular movies, school subjects) is likely to be more outgoing and start conversations. This is where your coaching is really helpful.

3. My kids always start taking in the car. I don't prod. I just wait. I listen. And like magic, they start talking about their day, their friends, the news....One caveat, though: ipods really get in the way of this!

4. One thing that helped my daughter TREMENDOUSLY!!!!! was involvement in a local theater group that has a strong educational component. Is there anything like that near you? She used to be TERRIFIED of phone calls and talking one on one with adults. But because of involvement with this theater program, she got comfortable with her voice, following a director's feedback and instruction, and opening up to others. She has formed lasting, strong bonds with kids from other schools and age groups, and looks forward to meeting with them at events outside of rehearsals and performances. It made the whole process of starting conversations with strangers, eye-contact, appropriate body language, etc, much easier for her.

4. TOASTMASTERS! Seriously, they have the real answers for the vast majority of us who get tongue-tied. Look up your local chapter to see if your teen is welcome, and go along if your teen says it doesn't make them more uncomfortable. You'll both get a lot out of it.

5. See if your local 4-H club participates in public speaking and presentations. I've seen kids who were nervous wrecks one year, go on to win state level competitions the following year because of the guided step-by-step process and support in these programs.

6. Does your school participate in Destination Imagination? It's another awesome program for getting kids comfortable with thinking on their feet and working together in a supportive environment.

I hope this helps.

Has he ever received any therapy for his issue? A speech pathologist might offer some help. You might ask your family doctor or his pediatrician for some suggestions.
Other than that it sounds to me as if you're doing a great job to help him. Confidence helps a lot too but it takes time to build up confidence. Are his teachers aware of his issue - good teachers should want to know of his struggles and then also to know to be patient and supportive when he tries to speak with them.

Hi. What grade is your son in? Does he have an IEP? Does he have any time when he sees a speech therapist? I agree that a processing difficulty may make it difficult to engage in spontaneous conversations and dialogues, and you're wise to help him "roleplay" and anticipate what to say in different situations. I think the "jury is out" regarding truly effective means to help processing speed difficulties, even though programs like Cog Med purport to help, but I've not seen independent data that shows the effects last over time....you might want to repost your questions on www.millermom.proboards107.com as I know quite a few other parents of teens (and one member who is himself a teen, named "Bros") can relate to your son's situation.