Some, but not all, PA programs require a standardized test as an element of the application. The two exams are the Graduate Record Examination General Test (GRE) and the PA-College Admissions Test (PA-CAT). Students typically take these exams in the late winter or early spring before they begin the application process. Each graduate school requiring these exams will use the score in different ways during the application process, from deciding who to interview to using scores when comparing similar candidates and more.
The GRE is a standardized exam similar to the SAT or ACT that is administered in high school. It has three sections that assess verbal reasoning, quantitative reasoning, and writing ability and takes about 3 hours to administer. It can be taken in a testing center or proctored on a candidate's own computer. Scores are available 10-15 days after the exam date and should be submitted to CASPA. More information available here.
The PA-CAT is an exam designed to assess the specific skills and knowledge necessary for success in PA programs. It measures general abilities and pre-req content from nine different science subjects. The 240-question exam is taken at any Prometric testing site. Allowing adequate time to prepare and receive scores is an important element of preparation. It takes 4-5 month of review and practice to do well, and exam score results can take up to 2 months to receive. More information about the PA-CAT is available here.