I like the point that implementing one of these methodologies is unlikely to make a disfunctional team functional.
From what I have heard of the experience at PSC ... a team which I think was working pretty well before ... moving to an agile approach has meant producing small, meaningful units of advancement in short periods of time rather than big bunches of advancement which only become available after a protracted time, but without losing sight of what is going on in the larger picture. I think this comes from having in mind a pretty clear vision of where one is going over a longer period at the start and keeping this vision in mind as one sets short term goals.
I.e., one has repackaged a working development process so that the work product is produced in different units, but the overall development team functioned before and after.
Some more I found worthwile reading on scrum:
And still more:
https://www.scrumalliance.org/community/articles/2010/december/the-land-that-scrum-forgot (uncle Bob)
http://manifesto.softwarecraftsmanship.org/ (addition to the agilemanifesto: "Craftsmanship over crap" by uncle Bob)
And still even more:
And yet more, why not:
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