Once of the nice features of SBG it that it really lends itself to the backwards design process. Using state standards to write learning goals, using learning goals to write assessments, and then designing instruction to support the assessments.
Because my academic standards assessments are 100% of a student's grade, if I expect that my students will do their assigned work, it had better be high quality and completely aligned with the learning goals. I have to convince the students that if they don't do assigned work, their grade will suffer.
I truly believe that homework should be used for students to practice skills that they are in the process of learning, and that if they make mistakes while they are practicing, they should not be penalized. Sports analogies are particularly apt: mistakes on the practice field are fine - it's performance in the game that counts.
I expect students to have their assignments done to the best of their ability when they walk in the door of my classroom. If they have trouble with a question, I expect them to reason through as much of it as they can and write down as much as they could figure out along with a note about their confusion.
I check assignments for completion at the beginning of the class period. I enter assignments into the online gradebook as either 'T' for turned in, or 'M' for missing. Students can fill out a small form to get the grade status changed from 'M' to 'T', although I make a comment that the assignment was late in the gradebook. Assignments are all in a 0% weight category. I enter this information mostly so parents can see their student's trend in assignment completion.
Students quickly find out as the school year starts that even though assignments are not directly part of their grade, they cannot attain high levels of achievement without doing the assignments in my class.
Cheating becomes a non-issue. Students usually copy assignments in other classes to get points for the assignment. In my classes, the only way for students to earn points is to learn from assignments and then show me what they know during an assessment.
As far as extra credit assignments go, there are none. What can you do to get your grade up? Study and reassess a standard. No word-finds in this class!