So you want the learners to learn what you want them to learn. You have chosen your learning targets and you have designed learning activities to engage them. You have taken the time to investigate what your learners already know so that you can build on their prior knowledge and experience.
Then you get started and it becomes clearly evident that the learners don't know what you thought they knew. You ask questions for clarification and you realize they really don't get it.
So then what?
Sometimes educators make assumptions about the prior knowledge of their learners. Sometimes we assume that just because a kid has finished 8th grade math, he is ready for algebra. We frequently assume that our own class knows what they need to know from our own prior lesson. We may even see data that tells us they know it! More realistically, the data tells us that the kid knew the right thing on test day in the manner that it was tested.
So they don't know it now.
As a teacher, what do you do? Undoubtedly, it is frustrating to work so hard "teaching" something, only to see that they don't know it at all later on down the line. How do you handle the frustration? Do you find fault in the students' work and their study habits, or do you look at your own work and determine what you can do better next time? Do you bring out what you have already tried or do you go find new and better?