These changes often are caused by miscommunication or misconception on the part of the students. Most likely this situation caused student to not perform as well as they might have otherwise. So your data (the grades) from the assignment or activity will reflect scores lower than you anticipated. This data set is a great starting point for a new SGO! Capture the data from your grade book (screen shot) and plan to improve that mean score with your next group of students. Document your changes to your assignment, lesson and presentation and you are on your way to a new SGO.
As you approach this assignment or activity again, be sure to document the different approach you took to assist the students to achieve better scores than the year before. Even if you tell the new students what the last students did wrong, that is a strategy and you are altering the their paths to do better. Once you have those new strategies for that assignment or activity, keep using them and move on to improve a different assignment.
Because I have this tendency to improve everything every time I go through the lesson, I really end up doing several SGOs but only document one. Hmmmm, maybe I need to rethink that so I don't run out of SGO options . . . Who sees a problem with that approach? Are SGOs slowing down progress or speeding progress up? None the less, keep up the great work!