Check the website for the journal in which the article was published. Most journals (academic, scholarly, or peer-reviewed) have websites that describe the journal, how authors can submit their research to be published in it, and the editorial and review processes. Find a journal's website by searching the journal's full title - usually something like "Journal of Biology" or "Journal of the American Biological Association." On the website look for information about peer review on pages like these:
Journals that the UMKC Libraries subscribe to electronically are listed in our eJournals database, which includes information on the peer review status of some journals. From the eJournals search tool (UMKC username and password required), enter the title of a journal in the search box. Click the title of the journal to see its information page. Look at the bottom of the listed information for an item that says "Peer Reviewed" to see if it says Yes or No. If the "Peer Reviewed" item is not in the list you will need to check the journal's website instead.