This article looks at the arguments put forward by J.I. Pozo in 'All that glisters is not gold: nor is eveiything that is learnt constructed (in the same way)' .It notes the existence of various constructivist options and draws attention to the fact that these options are used to explain particular situations without always taking into account the specific conditions of these situations. The author mentions the construction of knowledge in a formal educational setting, and notes several of its most significant characteristics: its social and socializing nature; material taught at school as pre-existing knowledge; the need to unbalance students' knowledge in an attempt to 're-balance' it. The article suggests that these characteristics do not present an obstacle to the construction of knowledge at school; their relevance to un adequate explanation of this construction process is stressed.