After teaching for 30 plus years I have many times gotten a new student who has been previously taking lessons from another teacher.  After talking and hearing them play its sad to me to see that my new student, after month and sometimes years of lessons, can not play a full song,  just pieces of many songs, can’t read music and wasn’t taught any simple rudiments of music or ear training or correct technique.  My small input for anyone playing any instrument,  If you can’t play a full song,  read or fully understand music after even a few months, do move on and find a new teacher,  I have seen it too many times where I am actually teaching someone who’s been playing for a while,  as a beginner.  I  put all these pieces together from lesson one.  So in a very short while they are playing full songs they love,  and if they want to have ear training and theory to really understand how music works (great for soloists and songwriters etc.) to really grow and enjoy playing the guitar and music on any instrument.