Well done. This is beautiful.
What electronic media do to choral music especially is so disappointing. It says a lot about the uniqueness of the sound of the human voice that despite the application of our best technology, we can do no better than "Choir Ahs" in duplicating it...or something as ghostly and odd as the
vox humana stop on a pipe organ.
Even so, I was able to understand what you were after here. My compliments to you on a perfectly lovely poem, to begin with. The music amplifies the sentiment of the text well, and there are some heart-rending moments. It's a pity your school choir couldn't perform this piece. It doesn't seem too difficult, especially omitting the optional notes...though school choirs can have difficulty with divisi passages and such. Frankly, only professional choirs could manage the highest soprano and lowest bass options, but obviously you knew that.
Measures 13-14 are magical, but followed by those parallel triads in 14, it seemed to me you might have done something richer there. By measure 15 you're doing more what I'd have expected in 14 following that lovely moment from the ladies. Likewise, measures 23-25 that beautiful descending tenor line (as a tenor myself, I love you!

), so fitting to the text, are worthy of a composer the likes of Jean Berger. It was a mature and very musical decision you made in giving that line to the tenors in their middle-upper register, instead of the altos in their chesty lower register - you seem very well aware of vocal quality as well as range considerations.
In measure 28 I see what you're after, but I really think you could have done something more creative and effective than having both the tenor and the soprano resolve parallel up to the D-flat...and I'm not just saying that from the point of view of a classicist. I just don't think it works here. Were I you, I'd have weighed whether it was more desirable to have the soprano melodic line continue up that scale, or let the tenors have their passing dissonance resolve up; in the end, I'd probably have let the soprano have it and I'd have taken the tenor down to A-flat instead of up to D-flat.
I really wanted to like what you did in measures 30-33, but all those parallel triads...I dunno. I think I understand the effect you were after...Rachmaninoff does similar things in his choral music quite effectively, including parallel triads, but he approaches it differently and uses it sparingly - and of course, he's Rachmaninoff, so it has a magic and sense of place that almost defies analysis. What follows in the womens and mens parts is superb word painting, though...very effective.
Anyway, I suppose what I'm trying to say is that this piece is so good, the few places where (IMHO) it isn't as good really stand out. To me, anyway. I realise you're not trying to follow any particular classical model, but even so there seem to be too many parallel triads going on here. Too much of that sort of thing makes it sound too 'pop,' and I don't think that's what you were after. There were also ways you could have filled out some chords and added richness without appreciably changing the harmony. I'll show you a couple of places if you like, but don't feel obliged to ask. This is an extremely personal expression, and I have no desire to intrude.
Congratulations on a fine work.