Ave! I've decided to try and get back into reviewing, so I started out on something I was sure would be of good quality - it had your name attached, after all, and in my experience that tends to indicate a good story.
My introductory flattery out of the way, I really, really like this. The idea behind it is fantastic, and it fits together wonderfully - Connie saying that a year for each region is about right, Reggie's visit, the way Marcelo's view of the world captures moments in hyperreality, missing nothing and embracing everything. I suppose the main point I'm trying to make is that I like it. A lot.
I have got a few suggestions for improvement, however, mostly to do with that last chapter, which it was brutally obvious that you didn't like writing much. The other chapters are fine, though they contain a smattering of typographical errors. For instance, in Chapter Two, you have this:
which should probably read:
or something like that. Actually, while we're on the subject of Chapter Two, I think Reggie's past spills out a little too fast, and in fact people seem to change a bit too fast in general when they're around Marcelo. Overall, the story feels to me like it's a little too fast-paced in places, especially given the way Marcelo seems to live slowly, in a world where there is always time to contemplation. Then again, maybe you're doing this deliberately, to comment on the speed at which the people he meets live. I'm not sure. I probably shouldn't have done this immediately after reading a chunk of The Pilgrim's Progress, because now I can't shake the feeling that everything I read is an allegory.
Moving on, we reach Chapter Three, which, although necessary, I wasn't quite such a fan of. Perhaps it's because I have a better idea than most of what it's like to be in a situation like that, but the scene with Phyllis and Marcelo didn't seem real to me. It definitely passed too quickly, I can say that much, and Phyllis acted totally unlike a doctor in her reaction to Marcelo. Even if she is human, even if she does have concerns and doubts, there's a line that doctors - especially those who work with children - are very careful about not crossing. They have professional standards.
Marcelo's reaction doesn't seem quite right, either. It's all right until he suddenly looks up at her, apparently recovering in an instant; there needs to be a little more time, a little more of a gradual change, and a little more relapsing into some kind of shock or sadness. I know he has a very unusual and surprisingly mature character, but there are some things that most people - let alone fourteen-year-olds - don't take that well to, and I think Marcelo might be taking it slightly too well.
Oh yeah, and using the word 'giggle' really kills the atmosphere. 'Giggle' is one of those wrecking-ball words that ploughs through tension with wild abandon, a lot like the phrase 'luminous pink'. I'd suggest maybe reconsidering it to maintain the atmosphere you built up.
Much of what I've said about the scene with Marcelo applies to the scene with his father: it feels a little too quick, and I don't get the sense that there are two real people arguing here. I get the sense that there's one real person (Phyllis) trying to get past a threshold guardian. Perhaps it's the way he doesn't seem to fight back hard enough, perhaps it's the fact that he hasn't been characterised much beforehand - which makes him the weakest character of the story - but the scene doesn't totally convince me.
That's not to say that this chapter wasn't good. I mean, it's still a fine piece of writing - it could just be better, and that's always worth aiming for. You said yourself that it was a very short chapter, 1600 words, and that's probably one of the reasons that the central thrust of it doesn't come across as wholly convincing: it doesn't have enough space to really be fully developed. I know what it's like to wrestle with a chapter you hate, and offer my congratulations for making it as good as you did - but equally, the fact that you hated it seems to me an indicator that you probably focused a little more on getting through it than polishing it to the smoothest possible finish.
Oh, and at one point Phyllis said this:
which, if I'm not very much mistaken, ought to be this:
Still, I like this. The very fact that I had so little to say about the first two chapters makes it clear enough that either it was excellent or I was blinded to its faults by the depth to which I enjoyed it - or both, which is what I suspect is the truth. The third chapter is a little rough around the edges, but still good - and of course, as I said, I'm likely to be a bit more harsh a critic when it comes to scenes like that than others. Overall, an excellent read, and I'm keen to see more of it.