I have been exploring online music notation programs and came across Noteflight and its subscription version Crescendo.
Noteflight is social networking for musicians! You have the capacity to create and store 25 scores online. It is great for collaboration and working together on composition projects. Students can make their scores public or private with various sharing options inbetween.
Noteflight is also great for private music tuition, K-12 education as well as tertiary level students. Visit http://www.noteflight.com/