HESI isn’t just one exam. It’s a suite of products, including exams, to help students prepare for their board exams (most commonly the NCLEX exams for nursing).
In most cases, individual schools select the specific HESI exams and prep-products that will be made available to their students. The products chosen by the schools include exams that can be taken before students ever enter the program, exams and prep-products offered throughout individual courses, and a comprehensive exit exam that covers the entire curriculum.