Teacher getting mad is just not right. I used to be able to read music, but not so much anymore. I found that 90% of the time, the written music was nothing like the recording due to improvisation. One example is my book of Steely Dan music. The written bass lines are just mostly roots and 5ths. So pretty much useless for learning the songs. I found that learning by ear was more true to the recording and then I could add my own flavor to it if I wanted to.