ROCK, POP, BLUES, FUNK.
Rock music as a study format is defined by it's simplicity and accessibility to students. Most younger people, and indeed adults, may not have listened to much jazz or classical music, where they are probably listening to pop music frequently. This means we can choose current hits that students like and use them as study vehicles. This has the great advantage of maintaining interest, and also that students can then play the songs to their friends for some peer admiration.
Rock differs from other genres mostly in it's beat which is solid and easy to follow. This makes it easier for younger students who may not have developed accurate timing. Like any other genre rock can lead either to virtuoso playing still in the rock genre, or often students will study rock and gain some technical skill which they may then use to explore jazz or classical music.
Variations on rock like funk, blues and progressive rock or fusion, are hybrid forms that usually contain jazz elements.