Cardboard Hill

[RiverNotch]

Two blocks down from school Here's where the loss begins.
by the boarded up house on Catalina, The first detail, the house, feels inconsequential -- the second indicates the loss real well, being something so specific.
we rode banana boxes and garbage lids I would think that the boards of the house would relate here.
down an icy face, grinning all the way. Something about "icy face" makes me think of a cliff rather than a steep hill, but that's just me.

One year we built a jump Again, that sense of loss. First, school, second, time -- but this depends too much on context regarding the author, I think. As much as it would be hard to believe a child would write in this style, the voice of the poem could still be considered so -- there's not enough clarity regarding the speaker.
that sent us flying uncontrollably "Uncontrollably" is not as good an ending as "flying", I think.
before landing in a pile of powder 
at the bottom of the hill. These two lines feel easily compressible. Where else would you usually land than at the bottom of the point, unless hills go in loops, or there's another hill on the other end, but those situations are unlikely; and "pile" doesn't add anything to the situation of the powder, since if the powder wasn't so stacked, then this would be less of a nostalgia trip, and more of a horror show.
 
John broke his arm testing it out, I agree with the above. "Testing it out" is superfluous. Perhaps a bit of detail on the arm?
but we told his mom he'd slipped on ice
so she wouldn’t spoil the fun. I thought of something Oedipal with these last two lines, but that's probably because I was striving to find something deeper from this -- the speaker is too oblique for this to be so clearly a nostalgia trip, and there are no deep thoughts to be derived here, either from a good turn of image, a sudden light from the title, or even some explicit declaration of depression at the end. This might just be a lack of experience on my part, but outside of the images and the brief nature of the story, there's nothing really poetic here for me, or at least poetic enough to justify eleven somewhat wordy lines.

That simplicity itself could be the point, though, but it still feels too simple, again for eleven lines -- or perhaps I'm missing something in the objects? But then, aside from the snow and as noted the whole mother thing, the objects don't signify for me too much, other than the overarching tone of simplicity with the banana boxes--

Hum. I suppose it's really sinking in, now. The image of flight at the center does make the fun of it all feel more brilliant, yes, and besides from the stark memory of that one name at the first stanza, the grins really do highlight the sense of loss. This is fair, but I think I have to repeat that I think this poem might be too long -- the last two lines of the second stanza again can be compounded into one, and to follow suit, the first stanza probably can be shortened, too. The two middle lines of that stanza, perhaps.

FINAL NOTE, REGARDING THE STATEMENT OF THESE LAST THREE PARAGRAPHS: Well, it finally sank in, the poem. It's good, talking about the simplicity of fun, as mercedes so rightly puts it above, but I do think it's a bit too long for its own good, especially with the symbolism behind the images being, to me, rather soft, or at least merely implicit. Two lines compounded at the start would make it better: the last two lines of the second stanza, as noted earlier on, and the two middle lines of the first, perhaps. 

---

"I adapted this poem from a conversation I read on a Facebook group for the neighbourhood I grew up in. Basically all the details were in there; I might start lurking other neighbourhood facebook groups to steal some more ideas."

That neighbourhoods long past have such facebook groups speaks to me more than the poem itself. Perhaps--