When he was 13, he was accepted to study at the Conservatorio de Valencia with the pianist and composer Vicente Asencio. Here he followed courses in harmony, composition, and performance. Yepes is credited by many with developing the A-M-I technique of playing notes with the ring ("Anular"), middle ("Medio"), and index ("Indice") fingers of the right hand. Guitar teachers traditionally taught their students to play by alternating the index and middle fingers, or I-M. However, since Yepes studied under teachers who were "not" guitarists, they pushed him to expand on the traditional technique. According to Yepes, Asencio "was a pianist who loathed the guitar because a guitarist couldn't play scales very fast and very legato, as on a piano or a violin. 'If you can't play like that,' he told me, 'you must take up another instrument.'" Through practice and improvement in his technique, Yepes could match Asencio's piano scales on the guitar. "'So,' he said, 'it's possible on the guitar. Now play that fast in thirds, then in chromatic thirds.'" Allan Kozinn observed that, "Thanks to Mr. Asencio's goading, Mr. Yepes learned "to play music the way "I" want, not the way the "guitar" wants." Similarly, the composer, violinist, and pianist George Enescu would also push Yepes to improve his technique, which also allowed him to play with greater speed.