Does anyone know?

I inherited my uncle's desk over 30 years ago. I cleared it of most of his stuff but there were a few things I left lying in one of the drawers because I'd no idea what they were and didn't want to just dump them. Tonight I was looking for picture hooks because I plan to put up some family pictures and I came across a wee pendant. It's about 3.5cms long x 2.5cms wide. I know it's a pendant because it has a ring to attach a chain to. It's silver - and I know that because it has a hallmark which (at the moment) I can't make out. And it's quite heavy.

Here's one side of the pendant:

I think that reads: KSB - or could it be RSB?

And the other side is: 

My father's mother Margaret came from a large family, as most people did in the late 19th century. One of her sisters was called Charlotte and she married a McGown. The story we were told was that he came from Ayrshire farming stock, although he became a seafaring man according to family legend. Charlotte and her husband had a daughter called Irene and her husband is the person my desk belonged to. Complicated, huh? I'm guessing the J in this inscription stands for James which is the English version of Seumas. 

But what is this a medal for? Attendance - I'm guessing perfect attendance - for what? School? Sunday school? Where was attendance so important that it merited a silver pendant? This was almost a century ago, after World War 1, when money was tight.

I'd love any thought from people. If this is a historical artifact, I'll happily hand it over to a museum which can record it and keep it safe.