In my introductory and (second-year) AP courses--high school--I give
credit for "practice" (worksheet) assignments only when each problem on
the practice is complete and perfect. [In other words, students are not
given credit for merely attempting problems, nor are they "downgraded"
for incorrect answers.] After the original due date for an assignment,
students are given a one-day "grace period" to make necessary
corrections, which are indicated to each individual student via Post-It
notes. Assignments submitted after expiration of the "grace period" are
docked credit, so as to encourage students to practice and perfect their
understanding in a timely fashion, but students have unlimited
opportunities before the "grace period" to attempt problems and
explanations without penalty.
An unexpected but beneficial feature of this system is the opportunity
that I receive to determine general weaknesses and misconceptions.
Individual support is still provided, but when a particular question
troubles a large percentage of students, I recognize a gap in the
instruction and can address the specific issue in class. Rather than
trying to anticipate which questions and concepts will require
reinforcement and remediation, I *know* when "everyone has trouble with
question 3", because I can see the reponses from students.