Kiting (edited)

[Achebe]

Kiting

In Bonniebrae a field is split by kills
and hedged by thickets on the southern side, ....I don't get the relevance of 'southern', unless it has some implications for wind direction. Sounds like meter filler.
a vagrant patch of long untended graves ....'vagrant' patches and 'untended' graves or variants thereof are abstract and have been used too often before in poetry.
and then the darkest forest man has known. .... the hyperbole of 'darkest' is unnecessary. I get it that you're trying to convey a boy's impression, but it sounds too deliberate, the strings show.

On a Spring day with wind just strong enough ...the 'Spring' and 'just strong enough' get me. The latter is using too many words, all meter filler. doing things 'on a spring day' or 'on a summer's afternoon' are cliched. Perhaps 'on a march sunday' or something of the sort would be better. But the line is not entirely damned - you can retain it if nothing else works.
to bloom a sail and launch a skiff we gathered -  ...anything better than 'bloom' would be nice. 'bloom a sail', 'sails blooming in the wind', 'sails bloomed like etc etc.' - cliched 
a score of us to test our skills at flying ...there weren't exactly twenty of you, were there? 'a score of us' is an easy way of slipping in two imabic meters...not fair.
kites like fauns might dance a mating dance. ...the first good line in the poem
I brought the finest kite you’ll ever see - ... meter filler all. Unnecessary, old fashioned hyperbole.
a hand-painted red komodo dragon ... at last, some detail
with double wires and a twenty-five foot tail. ...like 'double wires'

I slowly let her up and gave her reign
then deftly pulled her aft to paint the sky.
I spent two hours teaching her to roll
and slowly build to form a somersault. ...the action being described is light, airy, and totally at odds with the lugubrious meter you have chosen.

Then sometime after noon we traded places
and I was high above and breeching clouds - ...not sure what why 'breeching', but it gets cleared up towards the end. I think.
a just-fledged falcon drunk on swoops and dives, ....on re-reading, this line is not bad. I don't like the sound of 'just fledged' - sounds terribly harsh to me, but the idea of the boy becoming one with the kite is nice.
I spun and dipped held only by my line. ..nice. from 

But fickle kites don’t have the nerve for kiting ...nice
as men don’t have the buoyancy to fly ...come on
so who’s to say whose fault, the bridle buckled, ...ah. the 'breeching' connection. great.
the guy wire snapped, I keeled and then I tumbled
back home, my body broke against the ground. ....nice ending

Hi milo - not sure if the above is of any use. I loved the ending and the general idea of the boy and kite becoming one, but the regularity of the plodding meter, and some of the word choices, didn't do it for me.