One method that my teacher will use in the group class is to only teach the call part of say the 'A' section of tune.    She will then play the tune and have us only play that part when it comes around.  

Then she will play the response part and have us get that down... then will play the tune through and we only play the response part...

Then will follow same method for the 'B' part.

this works well for AABB type tunes.  

It gets easier as you build your earball muscles.  of course we are talking about 16 bars of music with repeated phrases.  but its amazing how difficult it seemed at first.  getting a bit easier though.  use to be like this...

of course it helps alot if someone plays it for you at a speed more like this...

as opposed to this...

really just a chance to share one of my favorite old time tunes.  😄

not to be confused with this... B part different.

or is it?? 

@elcbk said..."Black-eyed Susie" is a little different than "Ducks on The Millpond", though.  Suppose this could just be considered a variation with the different B part notes. 

my thoughts too.  If you search youll find them both listed and i havent found anything yet that ties one to the other.  probably Bill taught Sue and Sue taught Randy and Randy got the B part a little different either accidental or on purpose and called it one or the other.  again either on purpose or couldnt remmeber the name.  Thats me throwing a wild assumption out because i havent asked anyone or found an interwebs that lists anything.

Learning one by ear helps the memory for sure.   especially listening to it over and over again.  and things that whoever is teaching says when teaching helps.. like. the A part starts with an A arpeggio...then you walk down the scale.   litlle clues that for whatever hang around in the brain.  Or things like start with a fat 1 ( first finger covering 2 strings ) onthe D and A string.  Or things like...this one starts just like that other tune.   

sheet music is a big help too.  I think a mix of both is good.  Opens up a lot more to you.  outside of fiddle tunes i think its alot to ask to expect someone to listen to say a performance of a bach piece and get all that committed to memory like it was intended.  I know people do..which is even more impressive.

@elcbk said "...Think maybe I cue off the backing or something & zone out - like I'm playing on automatic"

I dont know..everyone is different.  I certainly agree with learning by ear as much as possibel.  I think what you said about cue off backing and zone out is exactly a skill needed when playing music with ohers.  I dont mean  zoning out as in not being in the moment..  But being able to not have to think about what youre doing and listening to everyone else along with yourself.  Being able to adjust i guess.  Its something i know that alot if not most that read this dont have an interests in.  And Its something im working on.  You are correct in that if you get a say..performance piece thats commercially recorded sorta in your head it can sometimes get in the way.  

But the part about learning by ear applies.  Listen to whats going on and adjusts.

As you said sheet music is a reference for this stuff.   A map of the notes.  Ill use it to remember what a tune was that was taught that i hadnt heard before.  Ill also always try and record it in the class or session setting and also search for different versions online.  

Nothing wrong or right about what helps any individual.  Sorta got off your topic I know and bottom line that youre trying to make is important I feel is..you have to listen to folk/traditional music to get it.  The feel is difficult to notate out. 

If anyone reads this that hasnt went to a session before and plans on it.  TAKE a recording device and use it after asking if its ok.   Use that to play along with later and as is the topic..learn the tunes from it if possible.  Thats the source youll be playing with.   If you dont plan on that.. find something you like and listen to that.