At the very beginning of the story, Piggy tells Ralph that he has asthma and that he's "been wearing specs since [he] was three." His willingness to reveal this, his weakness, so readily helps us to see right away that he lacks almost all social skills but is trusting of people, particularly anyone who appears to have authority. This is only reinforced when he says "They used to call me 'Piggy'..."
A bit later, while telling the group that they screwed up and didn't do things in the right order he says "the first time Ralph says 'fire' you goes howling and screaming up this here mountain. Like a pack of kids." In this way he begins to differentiate himself from the boys. We start to understand as readers that he is intellectually on a different level than the rest of them.