After being m.i.a for 3 and a half long (and frosty) weeks Mia's school jersey has returned! It turns out a kid named James confused the bold print "Mia" on the tag for his own name.
I think Luke reminding her to look for her jersey in front of her entire year group might have helped - it certainly raised awareness of the missing jersey. Poor Mia, hopefully she has learned something from this experience and will take more responsibility for her things :-) Pays to be an optimist....