In order to increase my students' stamina, I would first do a 10 minute stamina test. I'd have students read independently for ten minutes, tracking the number of pages they read, and writing a brief summary to ensure they weren't just speeding through. We'd then figure out about how many pages students should read in 30 minutes, making goals to either increase students' reading rates, or to ensure they maintained them over increasing periods of time. This worksheet was very helpful in making the whole process concrete for students, and provided space for all the math (trickier than you'd think). This is certainly a useful activity year-round, but especially in preparation for lengthy state tests.