Summon provides the opportunity to “Limit to articles from scholarly publications, including peer-review”
I have not been able to find any explanation of what is included or excluded in this category on the Summon site and I think Summon need to clarify just how they define this facet. First year Biology students are only allowed to use peer reviewed articles and I don’t want to recommend Summon to students and have them select non peer reviewed articles.

Most other databases simply allow for the choice of “peer reviewed only”