The vehicle used most often to assess student learning in studio art classes is the critique or work review.
Many students are afraid of speaking up or saying anything negative in reviews, because they believe that to do so is equal to attacking their peers personally. Students do not initially know what a critique is for, nor do they know what constitutes useful feedback. Students need to be taught on an ongoing basis how to talk about art work, and some critiques, especially those in intro and foundation level classes, should have that specific focus in mind.
Most studio art faculty in higher education learned how to critique student work from their own teachers. What little formal pedagogical training they may have had was probably directed towards creating a syllabus and executing lesson plans, not towards learning how to conduct an effective critique. If you feel like there has to be a better way to conduct your critiques, one starting point would be to read Terry Barrett’s Criticizing Art, and Buster & Crawford’s The Critique Handbook. Then try applying some of their principles into your own classroom critiques.