Have you noticed that he has low self esteem? Has his teacher ever mentioned anything before? As a teacher, I would never just send a letter like that home out of the blue. Where is the guidance counsellor located? Do you have to pay? In NSW it would be unlikely that any public school would have the resources for this so I wouldn't ever send a letter like this home anyway!
I think spending one on one time with him would be great, and valuing the things he already does but speaking as one with low self esteem, its often personality that makes us susceptible to it also. My brother and I reacted in 2 different ways to the sam upbringing- he vowed to prove Dad's negativity wrong and I just accepted that I was hopeless.
Sorry to ramble on.