This chapter focuses on the formative assessment practices of preservice science teachers (PSTs) in evaluating high school laboratory reports. In many Faculties of Education, PSTs typically have a course on assessment available in their certification program; however, this course is often of a general nature and does not focus on activities central to science education such as use of graphs, tables, and argumentation extending therefrom. The current study examined how PSTs provide feedback on high school student laboratory reports and the challenges they encounter in doing so. We describe their practices and thoughts about conducting this formative feedback and conclude with recommending that PST education programs have an assessment course focused on the explicit needs of science teachers regarding assessment in science courses.