I use MuseScore on PC and laptop.   Never yet found a really good 'phone app for editing....  I actually suspect I wouldn't use a 'phone app in any sort of serious way - it's good to have a large working area with lots of windows visible...

Musescore has a very extensive set of plugins as well.   The two I use are ABC import (for taking fiddle tunes from http://www.thesession.org which are 'notated' if you can call it that, in ABC format) - and - the MusicXML import - which I have used to successfully import files from Finale.  Oh - there is also a PDF reader which I used once or twice, but the PDF score has to be an actual PDF document, not an embedded image in a PDF file.

Some folks say MuseScore can be difficult to use, and maybe don't like the way the editor works on a "bar by bar" basis if you are "composing something from scratch" making it awkward to simply insert a note and have everything "shuffle along", but if you're using it just to do simple, multi-voice arrangements of existing pieces - it's a breeze.  And I suppose, once arranged, other students can just use it in play-mode on mobile devices ?

I actually spent - I think it was $40 at the time - on "Noteworthy Composer" before I discovered MuseScore...   NC has never been used since...

I'm sure you knew all that already - my ramblings probably didn't help - just sort of saying that right now, I can't think of anything better for your use....