Sonic Pi is a live coding music synthesizer. It's simple enough for computing and music lessons, powerful enough for professional musicians and free to download with a friendly tutorial.
Developed by Cambridge University Computer Lab, Sonic Pi was specfically designed for and built in collaboration with teachers for use in the classroom.
The creator of Sonic Pi has also written a book to go with it.
The Raspberry Pi Foundation has a website stuffed full of learning resources and projects to try out with the Raspberry Pi.
There are projects using Scratch, Python, physical computing, Minecraft Pi, Micro:Bits, Sonic Pi and more besides.
The project material is written with kids in mind and covers a wide range of computing concepts designed to support the ICT curriculum in England and Wales.