If you can't afford an acoustic piano, or don't have space, an 88-key, fully weighted digital piano can be used for several years, but the choice of digital piano is important, especially for lessons with younger children.

PINW recommends the Yamaha Arius series of digital pianos due to their good build quality, sound, look and simplicity. Children can be easily distracted at home if the instrument has too many sounds, buttons, or options to play with, so the most important thing is to get a digital piano with the fewest buttons, but the best sound, and weighted action. You'll have to get an 88-key, fully weighted instrument, so that does limit your options a bit.

Most of the piano methods we use incorporate ALL of the keys practically from the beginning. How is this possible? Well, take a look at for example Piano Adventures young beginner series. Many of the early pieces have the students playing on all of the black keys from the bottom to top, and this is an important stage for kids to get their bearings on the keyboard. Using a shorter keyboard will mean that the educational experience will be compromised. 

Either of these 2 models should work well. 

YDP-144

The Arius YDP-144 digital piano provides authentic piano touch and tone suitable for any aspiring pianist. The Graded Hammer Standard (GHS) action builds proper fingering technique for an easy transition to playing on acoustic pianos. PureCF sampling delivers expressive recordings of Yamaha's CFIIIS 9-foot concert grand piano. Damper Resonance digitally recreates acoustic piano depth when pedaling, while Yamaha's exclusive Intelligent Acoustic Control ensures a full, balanced tone at any volume. Available in either rosewood or black walnut finishes, the Arius YDP-144's 42 in. cabinet lends a classic piano look to any home interior.

YDP-164

Yamaha’s Arius console pianos are among the most popular and best-reviewed modern keyboard instruments designed for the home. And every year, Yamaha’s team of designers and builders make improvements up and down the model line. The YDP-164 is a 2019 offering in the middle price range, offering sound and features that align perfectly with the needs of many schools, homeowners and anyone who needs a handsome, beautiful-sounding and versatile keyboard instrument.