At higher grades you must be able to discuss with the examiner musical features such as texture, form, style, and period of a piece of music. My own web pages to help with these parts of the test at Grade 5+ and at GCSE are available here!
Keyboard or piano - What should I buy?
I’m often asked this question so thought I would note down some of the main points in for and against each choice. There are three main options – a keyboard, a digital piano or an acoustic piano. Whichever your choice you should also consider an adjustable piano stool.
Keyboards 
These have many good features including demo songs and the ability to add backing tracks and chords. They have large banks of sampled sounds, and you can get creative with multi-track recordings of your own playing. Many models also interface with a PC and USB devices for MIDI music file storage and direct input to composition or sequencing software. Secondary school pupils in the UK will be taught on keyboards in their key stage 3 and GCSE work so there are obvious advantages in having a similar instrument at home.
A good keyboard teacher will use the automatic ‘casio’ chords only at the very beginning and then progress to fingered chords, using the functionality of the keyboards to teach harmony and explore musical texture.
It would be advisable to seek the advice of a specialist keyboard teacher as to makes and models to buy. But if you are looking for something to support piano lessons, make sure it has at least 66 keys (a piano has 88) and has the option of fully weighted action.
Acoustic piano
Size is important so buy the tallest piano you can afford – both financially and in terms of available space. New pianos are described as 108, 112 etc cm – the height of the case gives a good indication of the length of the strings inside and therefore the depth of tone. Older pianos will be taller and possibly deeper as well.
Look inside. Make sure a second hand piano is reasonably clean inside. Check felts are not too worn, bearing a strong imprint of the strings on them.
Most modern pianos are ‘overstrung’ (the strings appear to cross over each other), which is what you want. An older piano may not be – making it look as though it has longer strings than it really does. Again, most new pianos will have ‘underdamper’ action (the dampers are behind the strings in an upright or beneath them in a grand) but there are a few relics that aren’t so check this for yourself too. It is actually quite difficult to see the sound board (the wood the strings are mounted on), but if there are cracks in this the resonance will be impaired and it will jump out of tune all the time.
With a few exceptions, avoid Far East and the former Eastern bloc manufactured pianos. Reid-Sohn are a notable exception to this rule being excellent and fair priced pianos. Kemble is a reputable British make.
Try before you buy. If buying from new, make sure you try the exact model you are going to get – even the same model may have a very different sound. If buying second hand, don’t be fobbed off by a dealer who says it could be cheaply reconditioned or would sound better after a tuning: tell him politely that you will come back and listen to it after it has been done!
Trust your own good judgement, and your own ears – do you personally like the sound from this piano? There is a huge variety of tone colour between pianos and none of these is objectively ‘better’ than another.
New or second hand, this is a significant investment. Anything from a dealer at under £1000 is probably not going to give lasting pleasure as your playing develops, and may actually do damage to your technique or your musical ear (especially if it goes out of tune almost instantly). So get help - a pianist will be able to tell you if the action on a piano is basically even and smooth (but again a heavy or light touch is also a matter of personal taste); a tuner will be able to tell you if the instrument appears well made and technically sound.
Digital piano
These have vastly improved in terms of touch and tone in recent years. If space is at a premium, I would not hesitate to recommend say a Clavinova CLP 240 or higher which you can get for around £1000 on-line. A digital piano will have some limited recording functionality – probably only a couple of tracks deep, and only a few songs will fit in its integral memory – but you can use USB storage devices to supplement this. Most have a limited but enjoyable range of sampled instruments – the range of keyboard instruments including pipe organ and harpsichord, perhaps wood bass and guitar.
The important thing to look for to support learning the piano is hammer weighted action and touch sensitivity. A good touch will then produce a rewarding tone. However I don’t think the makers go out of their way to sample anything but well played piano sounds – so it is quite possible to play with the touch of a baboon and still not produce a truly ugly sound. While this might sound an advantage in the short term (!) it can obviously damage your learning in the process.
It used to be that the super light touch of a digital piano produced weak and lazy fingers, but I think that objection no longer stands as long as you set the touch to one of the firmer settings.
I hope this information is useful. It will be perhaps painfully clear that these are only my personal opinions, and a great deal of ink has been spilt in the discussion of what instrument to buy, and not all of it comes to the same conclusion as I do.
I recommend the UK piano tuners association web site (http://www.uk-piano.org/) or the Associated Board teachers forum(http://www.abrsm.org/?page=teachers ) for more information.
Piano stool 
For good posture, physical comfort and freedom at the keyboard, do not neglect to source a good piano stool, too. Your stool should preferably be adjustable, and do test it out first to check it doesn't wobble and squeak when you use the pedals or rampage up the piano with speed and force in a quick run through of the Grieg piano concerto....
Take a look at this site for more information.