Assessing student writing assignments and providing effective feedback are a complex pedagogical skill teacher candidates need to master. Scarce literature has closely examined the type of feedback that pre-service high-school teachers spontaneously deliver when assessing student writings, which is the main goal of our study. In a sample of 255 high school teacher candidates, we examined the type of feedback that they provided when assessing two writing assignments that differed in quality. One thousand eight hundred thirty-five comments were analyzed and coded into 11 sub-categories. Results showed that candidates' feedback not only focused on task performance but also on the writing process. Although candidates provided critical and past-oriented evaluations frequently, they also crafted feedback in a neutral tone and included future-oriented suggestions. Further, feedback varied as a function of candidates' gender, academic discipline, and students' quality of writing. Teacher training programs may use this information to design resources to address nuances of feedback provision.