Ideally students should have a good piano at home. If you do not have a piano in your home, then access to a piano in another house or school should be arranged for a minimum of five times a week. Having two places to visit on alternate days might be more convenient.
Next Best Thing: A Digital Keyboard
If you do not have an acoustic piano, a good electronic keyboard that features full-size keys, touch response (velocity sensitive) would be a next best thing. Please be aware that an electronic keyboard is not a piano, but a different instrument entirely. Pianos and electronic keyboards respond to the performer in different ways and require different performing techniques. These classes are about the piano!
It is much more rewarding to play a good acoustic piano. The tone is richer, louder, sustains for longer and a performer feels greater satisfaction from the dynamic range and responsiveness.
A Hybrid Instrument
Most of the top-of-the-range piano manufacturers are offering acoustic pianos that feature physical mechanisms which also have a digital aspect as part of the design. These instruments offer the facility of practising with an acoustic piano and, at the touch of a switch, a silent digital piano which is heard through headphones. Such instruments offer a student a good instrument to practise on which has a real mechanism, real strings, real soundboard and which has good digital sounds for practising silently. This facilitates the student to be able to do repetitive practise without annoying the neighbours.
Avoid Toys!
It is important to point out that the very cheap digital keyboards which you may buy in a toy shop for 99 Euro, or less, are not best suited to practising for on-going progress. These are toys. Please do not think that they are sophisticated musical instruments despite the claims on the packaging and marketing. While they may serve as an introduction to the world of music, an instrument that is suited to daily practise is an investment in the education of your child. Please provide the best you can!
If you start with a cheap electronic keyboard, perhaps you should be thinking about getting a real piano in the future.
Ask your piano teacher for some guidance about choosing a suitable instrument.