This is really a very simple piece, for the ensemble. The mallet soloist(s) do have quite a few notes to play and making sure the melody pops out of all the notes (a la the 4th variation in Carnival of Venice) should be a priority.
Even though not difficult, this is a good piece for a holiday concert to show off your mallet players early in the year. This gives them something to work for and it is simple enough to not take a lot of rehearsal time.
Range, rhythms and articulations should be no issue for most middle school bands. The one issue many groups may have is balance. Whether played by a soloist or several mallet players, projection will be difficult and a young band is likely to tend towards covering the melody. Awareness of the solo part and consciously listening for the melody will be key to having success with this piece.
Anyone looking for a mallet feature for a winter program should consider this work.