The rhetorically complex concluding components of academic written texts often challenge novice writers, having to summarise their arguments and stance, and offer prospective comments on future developments concerning the subject matter. With an aim to elucidate the lexicogrammatical expressions of such prospective comments in essay conclusions, the present study adopts the system of modality informed by Systemic Functional Linguistics (SFL) to examine the conclusions of explanatory essays written by non-native English speaking associate degree business students. The analysis compares the modality expressions deployed in high-and low-graded essay conclusions, including modality types, explicitness, subjectivity and value. The analysis also investigates how the modality resources are combined for providing more than one comment in the conclusion. The findings show that high-graded texts have a more balanced choice of modality, less overly assertive features and more prospective comments, while they still require improvements on a more consistent deployment of modality features. This paper concludes with a brief discussion on teaching implications of the present study, in that writing instruction can make explicit the functions of different modality expressions and equip students with the linguistic repertoires appropriate for more formal and technical academic written registers.