The student can attempt the assignment on the day it is given and if they have any problems, they can receive extra help before the next class period. I believe that the biggest benefit of block scheduling is the length of class time. Longer classes allow for several different topics to be taught in one class period. It also means that the teacher can spend more time with individuals making sure that each student has a complete understanding of the subject matter at hand. For science classes these longer class times are almost a necessity.
Labs can be setup and completed in almost a single class.
Longer classes also mean that teachers are able to give more comprehensive tests. By doing this, students are better prepared for the much longer semester and final exams. Teachers also benefit from block scheduling. They are given more time to plan for lessons, making them better and more extensive. They are able to cover more material and teach with different styles when given this much time as well.