Over the past year I have had the opportunity (thanks to a spare period in the timetable!) to run a number of music enrichment/extension classes. One such unit I ran was a Year 4 mallet percussion group (who later dubbed themselves the "marim-bros"...bless them).
The class consisted of around 15 Year 4 students, most of whom were learning piano at or outside of school and were looking for opportunities to extend themselves in music.
The school was lucky enough to have two marimbas, two bass xylophones and a number of high quality smaller Orff-style xylophones (enough for one per student).
This weekly enrichment program gave them some consolidation in stave-reading, linking between solfa and absolute pitch names and also the opportunity to develop ensemble skills and showcase some performances.
The average lesson structure would begin with some stave-reading activities, such as my giant stave activities (eg. teams of students spelling out the word cabbage by standing in order on the correct lines/spaces) or quickfire reading where students performed rolls on their instruments and had to change note according to whichever line or space I was pointing to.
We would then do some kind of reading recognition challenge. I would write up a well-known song (some examples include Jingle Bells, Frere Jacques, or our hello song) without telling the students what it was. They had 5 minutes to play it through and figure out the song. This allowed me to offer extension tasks to fast learners ("memorise it!" "play it backwards!" "perform it while doing a one-handed ostinato!") while working with those students who needed support.
I then had a number of larger-scale works which separated instrument types into different parts and allowed us to explore ensemble aspects such as balance, blend, listening to each other etc.
We performed our programs at a few school assemblies as well as our school fete/Open day and the feedback from students and parents was really positive!
I had a great time arranging simple tunes such as Heart and Soul, Frere Jacques and Somewhere Over The Rainbow and I highly encourage you to start a mallet ensemble of your own if you're able - I saw tremendous progress in all of my students from that ensemble, even those who were already high flyers.