## 1 Introduction
### Peer Assessment  
Peer assessment and peer grading refer to the evaluation of students' assignments by their peers, under a set of criteria defined by the instructors, most likely in the form of an assessment rubric (the term rubric refers to \"a scoring guide used to evaluate the quality of students' constructed responses\" [26]; that is, a rubric lists the criteria for a piece of work and articulates gradations of quality for each criterion, from excellent to poor [27]; a rubric has three essential features: evaluative criteria (used to distinguish acceptable responses from unacceptable responses), quality definitions (describe the way that qualitative differences in students' responses are to be judged), and a scoring strategy (either holistic/aggregated, or analytic or rendered criterion-by criterion) [26]). There are two main drivers of the increasing use of peer assessment in higher education. On the one hand, the implementation of the Bologna Process and the European Higher Education Area, which emphasizes student-centered learning techniques and methodologies [28; 29]; on the other hand, the rise of MOOCs, where scaling of the assessment process is not feasible using other assessment methods (except maybe tests and multiple choice questions) [30; 31], especially in writing domains [32]. Peer assessment is considered an adequate assessment method in collaborative learning settings [33; 34] and a helpful tool to promote critical thinking of students, while fostering self-reflection about the work done. It is also common to use peer assessment in team-centered project-based learning methodologies, where students are asked to assess the work done by their teammates, or teams can assess other teams' work; in addition, it is also possible to complement self-assessment mechanisms to evaluate students' own work [35]. The type of peer assessment can also vary depending on the learning goals, contexts, and technologies, and can be used both for formative and summative assessment, using different grading criteria to define the final grade in the case of the latter.  
The main benefits of peer assessment are generally associated with deeper learning experiences for students through reflection and self-criticism, as well as higher student involvement with the course and with the team (as a consequence of their inclusion as an active part in the assessment and grading process), a better and deeper understanding of assessment criteria, and a higher perception of fairness through student empowerment [36; 37]. For the instructor, the main benefits refer to the improvement of the overall learning experience for students, but also to saving time. There are also critical views of peer assessment, mostly related to different perceptions between students and instructors about the assessment process regarding fairness, workload, or anonymity [38]. In [38], the authors state that proper explanation or moderation by instructors can reduce the perception of unfairness and that, when used for summative assessment, peer grading can reduce the perception of students of the value of their degree or, as [39] point out, to grade inflation and failure to differentiate high contributing students and their counterparts. Nonetheless, and using the particular case of Moodle Workshops, [38] argue in favor of using Moodle Workshops with a formative and summative approach.