The first thing to consider in chosing a Yamaha digital piano keyboard is key size. The keys need to be the same size as regular piano keys. Make sure that the keyboard is touch sensitive.
This means that when you play softly using less pressure the volume is softer and whren you play harder the volume is louder. This way you can play with dynamic control. Part of the beauty of the music is the change of volume. This may seem obvious but many of the low priced keyboards do not have touch sensitivity. We have seen students with non touch sensitive keyboards develop a "typerwriter" technique in their playing which produces a lifeless and boring expression to the music. This is a hard habit to break in students. Insist on a keyboard that is touch sensitive.
The second thing to consider is the keyboard having 88 keys. Piano music is written to be played on 88 keys and using less tha 88 will result in limitations. Also and just as important, is that the keyboard has weighted keys. Weighted keys are very similar to a real piano.
When you play a weighted key, the weight of the key has to be moved and this takes a good portion of your hands energy. This along with touch sensitivity will train your hands and mind to produce music that has expression and sounds good. It will also make it easier to convert to an acoustic piano when the student is ready to advance.
You will probably pay more for a keyboard that has 88 keys, is touch sensitive and weighted than less expencive keyboards but your hands will develope properly. You may want to look at a digital piano at Atlanta piano rental. These usually come with 88 keys, touch sensitivity, weighted keys and pedals. These typically cost more than keyboards and are not compact, however they will offer everything the beginner needs until they are ready for a real piano.
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