Messed around with an idea similar to this. Start the players off as "kids" with average ability scores and one good one. Then they choose which class they want to be "when they grow up". Separate out the the abilities and work through it.
Yours would be slightly different as you "gain" an ability as you go. Basically run into the situation and add the multipliers behind the screen saying "you thought that was easy/tough" depending on how far they succeed/fail. Keep them guessing.
- Abilities: All scores are 8.
- HP: Start at CON and then add 1/6th for each year completed.
- Feat: 5th Year
- Skills: 1 per year, starting at the beginning of Third Year, unless they have more than 6, then add 1 to each year (starting with the lowest).
- Class Abilities/Features: 1 per year unless they have more than 6, then add 1 to each year (starting with the lowest).
- Armor Proficiency: Cloth, Leather, Hide, Chainmail, Scale, Plate (in order). Offered on the year, but can be taken at any time after the assigned year.
- Shield Proficiency: Light (3rd), Heavy (6th), can be taken at any time after the assigned year.
- Class: Chosen at the end of the First Year.
- Weapon Proficiency: 1-2 Simple, 3-4, Martial, 5-6 Superior (must take Feat if required).
- Stat Boost: Given the number of points at the beginning of the year.
- Spellcasting: 0 level spells are learned in the Third Year. The remaining spells are spread out over the remaining years. Prepared spells are equal to the base number and improve based on the primary Ability Score.
- Movement is reduced by 5’ and increased to normal after the 4th year.
- Size: All characters are considered size Small until the end of their 3rd year, then they take on their normal size category.