You know why learning isn't "sticky" for most students?  The answer is not an oversimplification.  The truth is that we simply don't spend enough time reinforcing content and allowing for practice/feedback throughout the academic year.  This affects a student's ability to actually master content, and in turn, leads to poor academic outcomes - especially on standardized exams.  To be truly effective, teachers must integrate the "essential questions" throughout their process.  Otherwise, students will underachieve in the long-term.