Why do you have to learn to play modes for the ABRSM Jazz Piano Graded Examinations?

If you play the notes of a C Major scale but starting on D this is known as a Dorian Mode, if you start on G then this is a Mixolydian Mode. Although they use the same notes as a C major scale they sound different because the order of tones and semitones has changed. A different mode is produced on every note of a scale making seven in total. The most common chord progression used in jazz is known as the 2 5 1 progression, these are the diatonic chords on the 2nd, 5th and 1st notes of the Major scale (known as the Supertonic, Dominant and Tonic). In the key of C Major these chords are Dm7, G7 and CMaj7 and when improvising over this chord progression the Dorian Mode is used for Dm7, the Mixolydian for G7 and the Major Scale for CMaj7. In Grade 2 students learn the corresponding modes for the key of G Major and in grade 3 for F Major and so on. As the grades progress other types of scale such as Blues and Pentatonic plus other modes such as The Lydian are also added. Jazz musicians devote a lot of time practising improvising over common chord progressions using various scales and modes. It is important to relate scales and modes to chords and chord progressions to the appropriate key eg when you see the chord progression Gm7, C7 F Maj7 think 2 5 1 in F Major, think Dorian Mode on G, Mixolydian Mode on C and F Major Scale on F Maj7.