Probably the best free resource you can have as a Music teacher is MuseScore. I have ditched Sibelius and now I use MuseScore for everything. The main advantage is the community, there are huge amounts of material that you can download and adapt – I have not had to buy any music scores for the last three years. You have to spend some time just getting used to it – I suggest just copying out some music to start with if you are a beginner.
For students, this is really good for learning how to compose music. I haven’t used it with younger children yet, but we do use it with older students. One of our GCSE students wrote a four movement symphony and it was excellent. This year I am going to start experimenting using MuseScore with Primary students and I will blog on how I am going about this and how successful or unsuccessful it is proving to be.