When I began my student teaching and subsequently whenever I taught a new course, I quickly found myself delving into the content at a level that was very different than I had in the past. I found that an interest of a content did not create sufficient knowledge to teach the content. One thing that is apparent is that if we do not know the content well, we will not be able to teach our students well.
So, when you hear people say that if a student can teach the content back to you, they understand it, I believe that is true. Mostly, because I have experience first hand with the reality of the statement. I am guessing that you all do to. If you are struggling to reach your students, or have them retain information that you are teaching, the first thing I would ask is that you ensure that you are not asking students to simply use rote memorization as a way of teaching in your class. Secondly, move from having student do presentations to teaching the content.
Our students have sat in classes for years of their lives and have been a part of hundreds if not thousands of individual lesson plans by the end of their K-12 careers. What if we taught them the components of teaching them a lesson and held them too it? They would need to have an objective, teach the content, and assess the class to ensure that others understood the content at a minimum, and if they did not teach adequately, they would need to re-teach the content so that the class met the objective. As a teacher, you can conference with the student to review the lesson and where they need to improve. It gives students ownership in the classroom and provides them the opportunity to reflect on their learning.
Now, in the reality of the classroom, this is not an everyday strategy. It is simply a high-leverage way to visibly see learning happen. Having students teach transfers to the real world. When students learn to reflect on the content in order to teach it and in return are asked to ensure that others can access the content through their teaching, we teach effective communication skills. Think about a business presentation, a politician, or a broadcaster, all of these professions require us to think about our communication and assess if it was effective or not.