Abstract. Teaching via inquiry has been found to be a strategy suitable for the development of argument skills. The influence of the impartation of argumentation skills on the quality of the High school students' written argumentation was tested in the present study. Twenty written arguments in bio-inquiry papers were analysed by using two complementary tools: Toulmin's Argument Pattern to analyse the components and a modification of Toulmin's Argument Pattern to evaluate the quality of the written arguments. The various tools enabled us to pinpoint the differences between two groups: one group that did not receive scaffolds for constructing arguments and a group that received scaffolds for writing arguments. The findings indicate that impartation of argumentation skills improves the argumentation abilities and level. Students who received scaffolds for writing an argument wrote more and different types of arguments for each claim and wrote a higher quality argumentation in bio-inquiry papers.