You say your son has proven that he can do the work, but I would ask if he's able to do it independently and successfully. If he does it with an adult hovering over him, offering help at every task, then he may, in fact, not be able to do the work. A thorough evaluation should be done to make sure that he has no difficulty making sense of words, letters, or numbers. If there's no evidence of a learning disability, then he might have ADHD, which is associated with inattention, distractibility, and often (but not always) hyperactivity. Since these two conditions often co-exist, he could even have both, so a thorough evaluation is doubly indicated.
However, very bright kids who find the work too easy or too repetitive often turn off in the classroom. They focus their attention on activities or thoughts that are far more interesting and stimulating than schoolwork. They are often misdiagnosed as having ADHD or LD, when the real solution is making the curriculum more intellectually stimulating, multi-sensory, and experiential. Unless you rule out that possibility, then a ticket to the resource room -- unless it serves gifted-and-talented children well -- is the wrong ticket.
You ask about the effects of special education on self-esteem. If special education means, as it unfortunately still does in some schools, that a child is segregated into inferior classroom space, with kids with a wide variety of poorly addressed special needs, the impact on a child's self-concept can be devastating and long-lasting. On the other hand, a child with special needs who is left in the regular class without proper instruction can fall farther and farther behind, and this situation also can poke holes in even a good self-concept. If special education is really special, then it should allow all children to learn in the ways that they can, in environments that are conducive to learning, which can be a self-contained special class or the regular classroom with adequate supports.