This is no myth, my friend. Studies have proven it in the lab and in the classroom. In fact, the effects on memory, retention, increased test scores and GPA were so great, the 'geeks' of neuroscience have given this effect another name… "Superlearning".
Long before neuroscience came around, wise ol' Socrates hit the nail on the head with his statement…
"Music has a more powerful potential to educate than any other educational medium, because harmony and rhythm of naturally structured music find their way into the deepest depths of the soul and unfold its natural beauty and dignity." – Socrates
You may have experienced greater mental clarity and focus while listening to classical music before.