Sustained silent reading (SSR) is a form of school-based recreational reading, or free voluntary reading, where students read silently in a designated period every day, with the underlying assumption being that students learn to read by reading constantly. While classroom implementation of SSR is fairly widespread, some critics note that the data showcasing SSR's effectiveness is insufficient and that SSR alone does not craft proficient readers. Despite this, proponents maintain that successful models of SSR typically allow students to select their own books and do not require testing for comprehension or book reports. Schools have implemented SSR under a variety of names, such as "Drop Everything and Read (DEAR)", "Free Uninterrupted Reading (FUR)", or "Uninterrupted sustained silent reading (USSR)".[citation needed]