Leo's decision (and let's be honest, it's a pretty bizarre decision) to pose nude for a drawing class pairs beautifully with his (ahem) exposing himself in other ways, as he begins telling us his story. And soon it's all out there—the uncertainty with how much he's supposed to reveal; discovering an embarrassing secret he quickly scrambles to hide (dirty underpants); the hesitation behind the curtain just as he's about to bare it all; the realization that no matter how he turns or shifts, there's no way of avoiding the least attractive parts of himself being seen by someone.
Alma, meanwhile, attends a drawing class not as a model but as an art student—a gift from Uncle Julian. If Leo's narrative is about exposing himself, then Alma's is about first learning how to express herself. The title of the class, "Drawing from Life," is a pun highlighting Alma's entrance into adulthood and learning from her experiences. And if we really want to dig deep on this one, the teacher's urging her to "shade" (13.3) her drawings can be read as encouragement to understand subtleties in the world around her, not just see things as black and white. We get lots of layers to consider here, courtesy of Ms. Krauss.