How many times have you taught a lesson or listened to a student playing their exams on their instrument when they miss a fingering or forget something that you have told them about at least a dozen times before?  I used to get so aggravated at that, as though it was their fault alone that they were not paying attention the other eleven times I taught that fingering to the class.  What I had to come to terms with and accept is that unless I was totally on my "A" game when I taught the skill 50% or more of the students would not remember the skill during the next class session.  The same was true for teaching new instrument fingerings, new markings, or just about anything.  If you don't find a way to grab the student's attention during the instruction you are going to wind up reteaching things multiple times.

How To Increase Student Retention In Music Class or Band
So what exactly do we do to help grab the student's attention and interest long enough to jam that new concept into their long term memory?  In music class we need to do the same thing that general classroom teachers do, we need to get them using more than just one of their senses.  If all they do is hear you say how to finger a note they will forget it quickly until it has been reinforced enough through daily practice.  If instead you not only tell them how to finger it but also make them finger it and do a simple exercise to reinforce it, so much the better!  If you go farther and make them actually write down the fingering or definition of a term they will remember it even more quickly. 

One of the big blunders that I still occasionally do even today is that I catch myself writing in notes or fingerings for a student during a lesson.  Don't do it!  Make them write it in by themselves.  Just because you write something down in a book does not mean that the student will have a clue as to what you meant by it.  This is also a great time to teach students how to mark their music.  Remember that a majority of students, the first time they write in an accidental, will almost always put it AFTER the note that it is supposed to go with.  Take these opportunities to fix these little misunderstandings before they grow into larger problems later.

Remember to also consider the following recommendations.  True, these are fairly obvious to any experienced teacher, but they are still important to reiterate:

• Write it in the book -  I now require students to write in anything that I catch them missing when we play a piece of music.  If a student misses the A-flat in the key signature we write flat signs in front of every A (in pencil of course).  At first it is better for kids to have the crutch of the accidental while learning the fingerings.  Once the fingering is learned we can erase the accidental to help them internalize the key signature.
• Use the board-  Using SmartMusic or a music notation program and a video projector (plus a SmartBoard or other interactive whiteboard if you have access to one) have students play a line while looking at the screen.  Have students use a marker to notate wrong notes on the board and then finally have the entire group copy all of the markings into their music.  Check to make sure they actually write them in!