The first thing i would do with this is to dump the expository lump at the beginning of the story. Weave the necessary information into the narrative. Or form it as a narrative bit. Maybe a conversation between the headmaster and Mark.

Secondly, a thorough proofreading to catch some problems.

The basic storyline is good, but the lump of information at the beginning may keep some readers from ever getting to it.

A basic rule of thumb is that you need a "hook" somewhere in the first couple of paragraphs. What amounts to a history lesson is not a hook. Your first few paragraphs are pure exposition and they telegraph too much of the plot.

When writing, you have to remember that there are lots of things that YOU, as the writer, need to know but that are not necessary for the reader to know from the outset. Draw them into your world a little before you give them all the history and exposition.

Just my tuppence,
rose