AbstractThe present article tackles an analysis on differences and similarities between the program of study 1993 and thereform to the secondary education of 2006 in Natural Sciences. As well as, the interrelation between the programmaticcontent of sciences II and the textbooks authorized by Secretaría de Educación Pública (SEP) for the above mentionedsubject. All this, relating it to the indicators and the scientific competences evaluated in sciences for the Programme forInternational Student Assessment (PISA) in 2006, the purpose is to find the possible causes that intervened in theobtained results of the evaluation.