How to teach beginning arranging
The arranger is someone with an engineers mind. Someone who likes to take things apart and figure out how they work. Try encouraging students to arrange their favorite songs, as well as songs in their lesson book and see what happens!
Arranging is unique in the sense that it is sort of a hybrid of artistic expression and learning the music either by ear or by sight. No matter what the student arranges, the song has to be learned first through sight reading or by ear. The only exception is using chord symbols. Yet, even still, arranging cannot be done from the absolute beginning. They have to learn to read some music, or know how to do something by ear.
The early years
At the beginner level, it's a simple as encouraging them to change notes around. When only one note is played at a time in their music, and they are younger, try asking them to change the song however they want.
There are several things you can change in a song, including but not limited to:
For instance, instead of 2 half notes in a measure, it could be changed to 4 quarter notes. Instead of a G, they can play an E, etc. Instead of playing the song on middle C, they can play it an octave higher.
Encouraging things like this makes them realize that the notes on the page are not gospel, and encourages their creativity.
Of course, you can arrange songs played by ear as well.
Chords and Harmony
The sooner you can introduce chords the better. Take a week or 2 or 3 just to get themm good at the chords. It's a bit of a stretch at the beginning, but it makes for way better arranging. A good set of chords to introduce would be:
Notes and 5G 1A 1G
LH fingering 3E 2F 3D
1C 5C 5B
Name of chord C F G
Find an easy song that is just for the right hand, that can obviously be bolstered by adding left hand chords. Draw a box above every measure (or so), and ask them to choose a chord to go in the box for that song. They would play the chord as whole notes for each measure. Obviously, they would need a little bit of an ear to know which chord would be best and where. Help them choose chords at first if necessary. But a person who would naturally excel at arranging will just know which chord sounds best.
However, there are some guidelines that can be followed. For instance, if the RH melody were to play the notes: CEFG in one measure, then the C Major chord would most likely work the best, because most of the notes suggest the C Major chord. Things can get fuzzy in this line of thinking, but also look at the starting note of the measure. If the starting note of the measure is C, then a G major chord would sound bad. Demonstrate this by playing a G major chord in the left hand with a C note in the right. Show the clash of sounds. If the RH melody were to play the notes: DFGF. Then the G major chord would sound the best. (Obviously the F would make it a G7 chord, even though the left hand doesn't play it). If the notes in the RH were: CDEF. The F Major chord would work great, but then again, so could the C Major chord. So at this point, it comes down to preference. 2 chords per measure can be used when appropriate. Be suggestive as to their options, but try not to give them the answer.
The notes C, F, and G could be used in place of chords in the left hand if chords are too difficult to learn yet.
Introducing more chords
Eventually, once they have used the C, F, and G chords frequently, they can be taught other chords to use. A good one to add would be the a minor chord, in 1st inversion to make it nearest to the C major chord.
Feel free to go back to old songs that they already arranged and ask them where they could put the a minor chord at.
Eventually, they would want to be taught all the chords to be used. Write out, and have them practice writing out all the chords in C Major.
G A B C D E F
E F G A B C D
C D E F G A B
I ii iii IV V vi vii°
Go ahead and write the roman numerals too, but feel free to leave out explaining that till later. Explaining that they can use any of those chords in the left hand, while the right hand plays it's notes.
Arranging by chord symbols
Chord symbols are found in much music, from the children's song book of The Church of Jesus Christ of Latter-Day Saints, and pretty much all pop music. If you have a piano book of a bunch of Taylor Swift songs for instance, you will see the chord symbol above the sheet music. Those can be used to create the student's own left hand, rather than following what's on the page. It is obviously imperative to know what these symbols mean. Please read the following amazing article on reading chord symbols: http://musictheoryprof.com/2014/05/how-to-interpret-chord-symbols/
Using the chord symbols, there are all sorts of things that can be done in the left hand. The chord could obviously just be played as is. And at first, they need to practice just doing this. Eventually, the idea of inversions can be introduced. You would need to get their mind good at inverting chords. Have them practice a few chords with their inversions, going up and down: Root, 1st inversion, 2nd inversion, 1st inversion, root.
At advanced stages, the chord could be turned into an arpeggio. You could create a waltz pattern with the chord, an alberti bass, etc. The chords themselves could be messed around with as well. A "C" chord could be turned into a Cadd2 chord to make it more new age sounding.
For those more apt to sight read, you could buy a book full of their favorite songs with chord symbols. For those playing more by ear, you have a few different options. You could get the book, then play the right hand melody and record it for them. You could look it up on YouTube and let them just figure out the melody. And then, you could google "[song name] chords and lyrics." For instance, 'let it be chords and lyrics.' The first result is usually a website called "ultimate guitar." Peer users create chords and lyrics to all sorts of songs on this website. All you have are the chord symbols and lyrics. However, it's not always in the original song key, and sometimes there are errors. The top voted results are usually accurate, but are usually in a key that is guitar friendly. If you need the song to be in the right key, then just google "[song title] chords and lyrics in [key]".
Changing the chords into other chords takes experience with chords, but the general rule is if any chords have 2 notes or more in common with each other, they can replace one another's roles. For instance, if you are playing in the key of C Major, and you have a C Major chord, the Am chord could be substituted to make a darker emotion to the music (if you replace the first chord of the whole song though, it will effectively change the whole song to the relative a minor key). A "G" chord could be replaced by the Em chord. The F chord could be replaced by the Dm chord, etc.
It is fun to do this with the children song book, or any pop song.
To do this with music that doesn't have chord symbols is more difficult, because it requires analysis of the music to find the chords, and they are not always cut and dry. A "C" chord might actually be a C6, and there are passing tones that have nothing to do with the chord. Therefore, analysis will be covered in another article.
This has been an intro to beginning arranging. Take the general principles and try encouraging your students to arrange. Some will really enjoy it. Others will almost refuse right away. To those students that find passion in it, you will change their life with the concepts in this article.