Strength, prime requisite for fighters, modifies melee damage.
Intelligence, prime requisite for magic-users, modifies languages, determines save bonus for clerics.
Wisdom, prime requisite for clerics, determines save bonus for all classes except clerics.
Dexterity, prime requisite for thieves, modifies missile attacks per round.
Constitution modifies hit points.
Charisma modifies reactions and retainer morale and determines max retainers (divide by three, round up, and add one for every point above 14—so 15 gets 6, 16 gets 7, 17 gets 8, and 18 gets 9).
Prime Requisite Experience Points Bonus
Characters with a prime requisite score of 13–15 add 5% to earned XP.
Characters with a prime requisite score of 16–18 add 10% to earned XP.
N.B. If the kids want to make a character of a specific class, will let them swap the highest score into their prime requisite, or, if time allows, will consider trading 2 or 3 points for 1 prime requisite point as per Men & Magic (10) or Greyhawk (8).