Helping quiet 5yo learn to stand up for himself

Consider trying a KidPower Starting Strong workshop.  It teaches "People Safety Skills" and they have classes for kids with their parents on Saturday mornings.  We haven't done it, but have heard wonderful things from families who have.  One helpful thing is that it emphasizes the idea that these skills can be learned, just like learning to ride a bike, and if you're not good at them yet, you can learn to get better.    

I understand your goals to help your son articulate his feelings and set boundaries. But my question back to you is, Shouldn't the adults in the environment be setting boundaries with the kids who are "grabbing things out of his hand, shaking him by the shoulders, pushing him out of the way to get to something, breaking something he has built, etc."?? He's 5. Learning to set boundaries and articulate feelings is important work. I imagine the work is made harder for him given that (based on your description), he doesn't appear to have adults around that he can count on to set and follow up on clear boundaries. Shaking by the shoulders, pushing out of the way, do not sound like "friend" behavior to me. It doesn't seem right that he should bear the full burden of boundary setting in a classroom experience at 5-years-old. 

I shifted from “modeling” to direct coaching,  for example, I would lean over and say quietly to my son “That boy just took your toy.  You go and say ‘that’s mine, may I please have it back?’”  Then I would gently move him toward the “taker” and coach him during the interaction, in his ear if necessary.  Now that he is older, when other situations have come up, I try to talk him through the actual interactions with words. Not strictly role play (I find that tedious), but more concrete than modeling.  Good news - he is now 11 and navigates all kinds of situations with a combination of verbal conflict resolution or simply getting/staying out of a bad situation. 

I think that having him “use his words” as you have done is a great way to have him learn assertiveness. Also the adults in the room need to facilitate this lesson in how to get along . If kids are being aggressive they need to know that it is not ok and to be given new ways to communicate. Martial arts will just give them an excuse not to use words but to react physically which is what kids, especially ones who find verbal communication difficult, automatically do. They need to learn verbal communication of their feelings. “Can I have a turn when you’re done?”, “Sure”!

Martial arts or sports teams (i.e. soccer) would be great for this.  Martial arts teaches confidence and gives one ability to defend oneself, which is valuable and my son benefited a lot from it, but I know it is not for everyone.  I feel that my son got even more confidence and social skills by doing soccer (and the benefit will be there from other spot teams as well).  It gave him a guaranteed group of friends with who he had something in common, the kids learn to support each other, and gave him an opportunity to practice social skills and being more self assured by going for the ball when one sees an opening and speaking up when something is not to his liking.  I tell my son that he is responsible for his actions and nobody can tell him what to do (except for adults with authority over him like parents, teachers, coaches, or police, etc) and he needs to tell anyone who tries to boss him around that it is his decision.  As my son entered school (he is 7 now) and matured, it became easier to teach him stand up for himself and to complain when someone does something he does not like, but that type of personality often translates into a "follower" which is dangerous when he is surrounded by kids who might be a bad influence.  I would recommend that as you teach your son self confidence and to speak up when someone does something to him he does not like you expand the conversation to cover speaking up when someone does something that he thinks is wrong or at least not to join in and follow along.  We just now got him to a point where he thinks before acting and does not blindly follow his friends, and he has a really tough time figuring out when he should "snitch" and tell the teacher and when he should just say "this is wrong and I'm not participating" and walk away.  Good luck.  Parenting is tough. 

We were concerned our son would have difficulty advocating for himself as well. He experience some of what you describe, but I think it hurt us more than it affected him.  This was in a corporate day care (Bright Horizons) and private pre-school. But once he got into public kindergarten, I think the combination of a more diverse set of kids and just maturing, he seems to have learned better ways to navigate these; and he's become more aggressive himself. We did work with the teacher to emphasize these skills; and like you we try to model helpful behavior- getting a teacher to help (something that was taught to us as problem solving early on at the toddler day care). And I'm hoping he and I can do aikido soon.  HTH.