Over at the Hill Cantons, there's a post about an OD&D hack that works well for students in his creative writing class. You can find the rules here.
I want to try these with my son - I think he will be able to grasp these, especially the fighter types.
Being so small, of course, I have this temptation to add a Thief Class. You have a fighter class, you have a spell slinging class, now, a class for the rest of us that get by with certain survival skills.
Cutpurse: 1d6 hit points, search for hidden items, secret doors or traps by rolling a 2 or less on a d6, hits as 4th level OD&D MU
Rogue: 2d6 hit points, search for hidden items, secret doors or traps by rolling a 3 or less on a d6, hits as 8th level MU
Guildmaster: 3d6 hit points, search for hidden items, secret doors or traps by rolling a 4 or less on a d6, read scroll by rolling 2 or less on a d6 hits as 12th level MU
Thief (pick one)
A. Leather Armor, Sword
B. Leather Armor, Dagger, Bag of Holding
This is just off the top of my head and may ruin this elegant system. Just had to throw it out there.