It is often the case that undergraduates writing essays to fulfil course requirements have an academic audience (i.e. lecturer/s marking the essay) as their target readers. These texts may represent a form of academic writing by novice writers in the process of learning academic discourse and conventions. Though these texts may not be comparable to professional academic writing, the aspect of the maintenance of a good balance between objectivity and the portrayal of an evaluative stance is of interest in this genre too (Hunston 1989; Hunston and Thompson 2000). This paper investigates undergraduate students' efforts to portray a contrastive stance through the strategy of problematization (Barton 1993) in argumentative essays. More specifically, it compares how writers of high-rated and low-rated essays problematize issues in more or less effective ways. Using the "engagement system" of the Appraisal framework (White 1998; Martin 1992; Martin and Rose 2003), this study analyses the evaluative resources used by the writers to achieve more or less successful problematization of issues discussed. The results indicate a more strategic and appropriate use of evaluative resources by the writers of high-rated scripts to create clear lines of contrastive positions. On the basis of the analysis, some pedagogical implications are discussed. (Contains 4 notes and 1 table.)