So the conclusion is a mixture of hope and despair.  The excellent briefing I received from ABM warned me about this - one's mood swings between feeling that one can solve all the problems of the school, if not the whole country, by the end of the week, and feeling that it is utterly futile to make any effort to achieve anything.  The truth of course lies somewhere between the two - one can in a small way provide very genuine help and assistance, some of which will be wasted or will fade when one leaves, but a part at least will remain.  Certainly everyone gains from a trip of this sort.  The school benefits from and very much appreciates outside advice, assistance and donations, whether of time, skills, money or equipment.  I certainly gained vastly (except in weight - I've come back a lot fitter and lighter!)  At one level, I've received many marvelous presents including this massive and beautiful crocodile (and I confess to dissolving utterly when the school presented me with this  as I was leaving), but more importantly I've gained many friends and many memories, and I've developed an appreciation of a different culture that is far deeper than can be achieved by merely visiting or travelling. 

I can also better appreciate the vastly greater opportunities and resources that we have in first world countries, and feel even more amazed and ashamed at our utter failure to do anything useful with these opportunities. 

The comment I most treasure came in a letter that I've received since returning:  "There are not many white men who would easily become one of us.  You have been one."