score:14
The "persisted for at least a few generations" and "conscious educated decision" requirements really nailed the coffin in this case. Especially that latter. It is not altogether uncommon to find organised states collapse; while the result might meet some definitions of anarchy, none of them really made a "conscious educated decision" to practice anarchism.
The most promising, closest thing I can think of is Makhnovia, but that only lasted three years. It did however seem to be a conscious choice to create something akin to anarchy.
If the requirement for "conscious educated decision" is removed, then I think a good example is the Kowloon Walled City. It was technically retained by China after the rest of the peninsula was leased to Britain; subsequently the authority of neither was in force in the region. So there was no formal rules or government in that region for decades.
By even less exacting standards, Medieval Iceland is often cited as an successful example of anarchy. That would seem to be a farcry from what you're asking for though: while decentralised, they had chieftains, laws, a judiciary and a legislature.
There's also examples where a state or empire collapses and local governance reverted back to tribes. However, generally speaking, even in tribes the people obeyed chieftains, elders or shamans. The primary difference between that and organised states is that their powers were not generally formalised, but rather depends upon their personal prestige. Disobedience was unpunished in the same sense that the state might drop charges against an accused for various reasons.
I'm excluding all the various intentional communities in this answer, because they typically remain subject to the laws and governing powers of the state they reside in. To my mind, they might have removed the hierarchy at the local level, but nevertheless remained part of the national hierarchy with the central government at the top. And also, because they tend to appear to me as a form of the ancient Greek/Roman direct democracy than truly a government-free society of implicit agreements.
If you think those qualify though, there are longer lasting examples such as the Stapleton Colony, the Twin Oaks Community, the Danish Christiana, or the Acorn Community Farm.
Upvote:7
While I wouldn't posit this as a successful example, the Mu'tazili in the 9th century makes for an interesting anarchist school of thought
Patricia Crone: Ninth Century Muslim Anarchists, published in Past and Present (No. 167, May 2000)
The Mu'tazilites offered a variety of arguments in favour of anarchism, but only one is quoted in full, that of the Mu'tazilite ascetics.It went as follows. Islam is different from other religions, for other religious communities have kings who enslave their subjects, but the Prophet was not a king, nor were his successors, and if an imam were to turn into a king, by ceasing to govern in accordance with the law, then the Muslims would be legally obliged to fight him and depose him (as the activists said). But civil war was indeed terrible; it split the community and led to more violation of the law without guaranteeing a better outcome (as the quietists said). Since imams kept turning into kings, the best solution was not to set them up in the first place. The Mu'tazilite ascetics did not deny that there might be a legitimate ruler in the future: they seem to have thought that he would have to be an 'Alid, or in other words a descendant of the Prophet.38 But in the absence of such a ruler it was better to have none.