There is an interesting and useful approach to learner-centric education, which circumvents many of these issues, and remains empirical and practical: Its the 'non-method' of Maria Montessori. She had a neat approach, and when asked "what is the Montessori method"? she said: "There's no such thing, just follow the child". [... which resonates with Bruno Latour's 'Actor-network theory', if you're interested in research methodology].

She spent many years following children, and trying to tempt them into learning with wonderful (3D)'learning objects' that she created, most spectacularly the Trinomial Cube [http://www.montessoriworld.org/sensory/strinom.html], which is a 3D instantiation of the Trinomial Theorem (there's also a Binomial Cube). The pity is that many 'Montessori' teachers dont follow either her advice, or the childen, and even fewer of them have the mathematical imagination to create a multi-coloured Trinomial Cube.