Ζαν Πιαζέ

http://tvxs.gr/news/paideia/zan-piaze-%C2%ABo-froint-tis-sxolikis-taksis%C2%BB

http://el.wikipedia.org/wiki/%CE%96%CE%B1%CE%BD_%CE%A0%CE%B9%CE%B1%CE%B6%CE%AD