Suggestions to Boost Self-confidence in 6-Year Boy

Hi Gals -
I am hoping that some of you have some suggestions for groups or activities in the West Michigan area that might help our 6-year-old build his self-esteem and become a little more confident with himself. He is the sweetest kid, but often shuts down or removes himself from activities that seem "too hard". He becomes frustrated very easily and can quickly be brought to tears because he "thinks" he did something wrong (especially when it comes to schoolwork or activities).
He has had a bumpy couple of years and really deserves a chance to just be himself and enjoy being a kid.
He went to a private faith-based school until February of 2008. We decided to move him to our local elementary in Grandville and thankfully were able to pair him with a wonderful teacher who took the extra time and special interest he needed. Unfortunately the curriculum differences left him very behind the students at his new school. Also, his birthday is June 1st, so he just turned six and was very young to be dealing with the changes and challenges he did. Based on a number of factors, he will have the opportunity to experience kindergarten again and hopefully feel more on level with the kids his age.
Another factor is his size. Although he was young for kindergarten, he was one of the biggest kids in his class. Currently he is just over 4 feet tall and weighs more than 70 lbs. He enjoys being active and we encourage outdoor activities, but again, he gets frustrated or tires easily and will give up if we aren't right there forcing him to stick with it.
In addition to his school and size challenges, he is split between two households (he is a step-son to me; my husband and I were married when he was 6 months old). He spends 3 to 4 days per week at each house and we all work very hard to keep doors and communication very open. Although we all get along and work hard to surround him with positive energy and experiences, I'm sure to a six-year-old it can still be confusing at times.
Also, in the midst of it all, his youngest brother passed away in January of 2008 (he had been in a hospital 2 1/2 hours away since birth, so our six-year-old’s time with him was limited). Although his conversations about his brother are sweet, thoughtful and positive, I can only imagine the toll such a loss can take on a shy kindergartener. (We did do some family counseling after Rocco passed away).
Anyway... to make a short story really long...
Clearly he is very loved. We only want to provide him any extra opportunities we can and help him to grow and thrive as a happy and healthy young man.