This article deals with the study of natural sciences in non-compulsory secondary education from the end of the nineteenth century until the educational reform in 1970. We begin with a critical review of the ways in which the secondary education curriculum and textbooks of this period conveyed established knowledge about natural sciences. We then examine the evolution of natural sciences textbooks and successive editions thereof produced by different publishers in terms of their design, structure, content, and context, methods which are complemented by information concerning authorship and commercial viability. We conclude by arguing that, since textbook publishers did not undertake substantial innovations between 1970 and the mid-1980s, traditional nineteenth century natural sciences school knowledge prevailed into the 1990s.