There are a variety of different keyboards available which are very popular with students taking GCSE Music. I will go through a couple of different options below to give you some ideas on could be suitable. We mainly stock both Yamaha and Casio keyboards, and so I generally say that depending on what you need the keyboard for will help determine what brand to go for. Yamaha are focused on delivering a high quality playing experience with their realistic sounds and voices, whereas Casio usually focus more on the digital aspect side. You will find that Casio keyboards have slightly better connections and recording/mixing features.
This keyboard is one of the most popular Yamaha models that is currently available, due to it containing some very high quality, realistic instrument voices and accompaniment styles. You do get a recording system built within the keyboard, and due to the 2 x 2.5W speakers, an impressive sound is produced. In terms of connectivity to a computer for composing etc, the keyboard has a USB to HOST input. All you would need is a standard USB cable, and this would connect the instrument and computer together. With this model, you are getting very realistic and accurate sounds, all from the reputable manufacturer, Yamaha.
I think of the CTK-7200 as more of a digital/mixing keyboard. If that is what you are mainly looking to use it for, then I think that this would be better. The voices are still of high quality, but the keys are slightly improved, as they are 'boxed'. This adds a slight weight to them, which makes them feel a bit more like acoustic piano keys. In terms of connectivity, we generally find that these are slightly easier. And better to connect to a computer, and offer a wider range of digital functions.
Of course there are many more models on the market to explore. I think these two keyboards show you what the differences are so you can look into what you need to use it more for.