In most courses the assignments are level. The information across assignments is different, but the level of difficulty stays somewhat consistent. Unless there is a clear jump (such as between a regular exam and a comprehensive mid-term), students assume that they did the last assignment well and they know everything they need for the next assignment.
This is not true in second-semester freshmen composition. The course is scaffolded, so that the easier assignments are earlier, but the assignments throughout the course get increasingly harder, even while building on previous assignments.
Students in writing (and other) classes assume that the first assignment will let them know how the teacher grades and that the next assignment, done the same way, will allow them to earn the same grade.
This is NOT true when the assignments are scaffolded. Each assignment increases the level of complexity. That means that if the student does not learn and apply the requirements in equally increasing complexity, the grades will decrease with each assignment.