The aim of this research was to establish the effects of argumentation and the quality of arguments related to history of the development of organic chemistry: (i) on the level of the pupils' knowledge about the composition, structure and general properties of organic compounds; and (ii) on their perception of the key aspect of NOS that scientific knowledge is tentative. A quasi-experiment involved two parallel groups of 14-year-old pupils, a total of 105 of them. The pupils in group ?, as opposed to those in group B, were exposed to argumentation in the context of history of the development of organic chemistry. The instruments in this research were a diagnostic test, used to establish how well matched the groups were in terms of previous knowledge, and a post-test, the purpose of which was to establish the effects of argumentation on the pupils' achievements. After both tests, the pupils expressed their views of the fact that the scientific knowledge is tentative using a five-point Likert scale. All the arguments produced in group A were classified in four categories based on their structure. Although a moderately positive correlation between the quality of arguments and the post-test achievements in group A was established, no significant difference between the arithmetic means in the post-test in groups A and B was found. After the intervention, a significantly higher number of pupils in group A were of the opinion that scientific knowledge is tentative, compared with the number of pupils from group B.