The nature of Ralph's mentality and developmental problem is very ambiguous. Although it is easy to pass off Ralph as a mentally challenged child, there are many things which show that this may not be the case. Ralph is quite capable of acting in a normal manner, he once in a while even makes very valid and sensible points. Oftentimes his bizarre behavior is attributed to his wild imagination. Ralph's behavior and difficulty in school is highly reminiscent of a few childhood psychiatric disorders such as severe autism, sluggish cognitive tempo, and some others perhaps as well, all of which are not impediments of intelligence but rather of social and environmental development.
Ralph often makes metaphors for things to explain to himself how the world works around him, such as describing shutting down the Nuclear Power Plant to avert a meltdown by comparing it to catching a pixie and wrapping it in tinfoil. This is a quality often associated with children who have a mild case of autism or perhaps attention deficit disorder, and also by children who have a very high degree of creative and artistic intellect. One could even say that Ralph has either a very unique perspective of everything, or he simply can't word out what he's thinking easily. As such, Ralph could be many things from a mentally disturbed child, to possibly even an artistic genius which brings up the subject of his prowess in performing arts. Ralph is consistently shown to have a high degree of latent creative and performing talent.
Aside from his role of Washington, Ralph apparently impressed Marge a great deal with his portrayal as Sir Lancelot and his acting exploits are referred to a few more times. His talents don't stop there either, he has impressive talent in singing (comic story Faking the Band), dancing ("Last Tap Dance in Springfield"), critique ("Fraudcast News"), he draws very often and in the comic a substitute teacher insists that he is an artistic genius due to his tendency to speak in haiku. Despite his supposedly subpar level of intelligence, when representing Canada at the Model UN club, he actually knows the words to the Canadian anthem as seen in "Das Bus." Although he has botched up on stage occasionally as well, generally it's strongly implied that he has genuine talent. Ralph also seems to be aware that he isn't "normal".
Children who are highly gifted in creative and artistic intellect are often mistaken by school officials to be mentally disrupted. Ralph is often used as satire to poke fun at modern school's tendency to misjudge young children in this manner, as well as their inability to give children special attention they need due to budget constraints. Regardless of everything however, in the end The Simpsons can be just as random as Ralph himself. Much like the case with every character on the show, it is ultimately up to the viewer to decide what Ralph's true nature is.
