Missing students

Last night in class, I was thinking that I really miss some of our students that no longer train with us.  I also miss some of the people that I have trained with throughout the years.  Some no longer train because they moved, which is an acceptable reason.  Some no longer train because they can't find the time.  Some no longer train because of financial reasons.  Some no longer train because they weren't having fun or enjoying classes anymore.  That worries me.  Do we need to always have fun?  I believe that answer would be NO.   But what can we do to make learning the techniques and forms more enjoyable?  What can we do to make classes more fun but still get the required learning accomplished?  There is a fine line between just allowing the kids to play and being too demanding.  Part of what we are hoping to accomplish during this Ultimate Black Belt Test journey is to better ourselves, thereby bettering our teaching and our school.