The present paper aims at investigating the structure and the content of the written explanations produced by primary school pupils' aged 11-12) during teaching sequences focused on the didactic elaboration of obstacles regarding temperature and heat. At first, teaching sequences targeted at the pupils' destabilising, restructuring, and identifying the obstacles were designed and implemented. Next, the pupils' written explanations were analysed with respect to their structure and content. The results of the analysis indicate: (a) the differentiated levels of pupils' written explanations with regard to their structure and content, (b) the evolution of the levels concerning the structure and the content of the written explanations produced during the teaching sequences and (c) the relation between the levels concerning the structure and the content of pupils' written explanations.