A good structure to a session is invaluable in the planning process. The pupils know what is going on and the teacher keeps track of time and can evaluate the efficacy of the session. Of course each session can have its own individual structure but as a basic template what I would suggest is:

1. Get comfortable. This can be listening, chatting or just about whatever you like but music can feel uncomfortable as it can expose you psychologically in a group however well you know the situation. A bit of arrival time, or maybe even a lot of arrival time can be very useful. In a 1 hour session, just listening to a 5 minute piece of music at the beginning might be an ideal way to get a common sense of purpose.
   
   
2. Learn something. This is the technique moment. It could be to do with getting to know a new instrument, a new way of making music or learning a new song. The crunch is that this new idea should provide a springboard for the next stage.
   
   
3. Creative work. The previous activity should have ensured that pupils have a tool to create with so here is the moment where, either in groups or individually, the new stuff is done. Composing a whole piece or just a tune. Writing lyrics for a song. Making a storyboard to go with a piece of music that the pupils are listening to. This is the real meat of the session.
   
   
4. Pulling together. If people have been working individually or in small groups, this is the time to pool ideas and listen to each others work. Maybe pupils have been developing different ingredients to fit together to make a larger piece...
   
   
5. Listening/Discussion/Listening. You might want to chat then listen or listen then chat. The order of this phase depends very much on the particular group and the material that you are working with. The only direct suggestion   would be to end a session with music rather than with words.