Training is the process by which a leveled trainer teaches an unleveled person, called a trainee. By this process, the trainee literally gains experience, and thus XP, over time. Through this XP gain, the trainee can eventually count as combat-trained, or even reach 1st level in the trainer's character class.
I will first describe the mechanics, and then discuss implications and possible expansions for these rules. Examples will be presented as we go along.
The base age for a player character in my game is 15; a random figure is added to this based on the character's class, to represent time spent in training. For fighters this additional number is 1d4 years, for mages this is 2d6 years, and other classes have other figures. We'll call this roll the "training dice."
Unleveled persons start at -1500 XP. They become combat trained at -1000 XP, and gain 1st level at 0 XP. Thus, between totally untrained, and freshly 1st level, one must earn 1500 XP. We can conceive that this XP is earned slowly, over time, through grueling effort and practice. The idea is that we are going to apply the training dice at a monthly interval in order to determine how much XP the trainee has gained from training that month. But how much XP will the roll represent? Depends on the class they are training in, since each class has a different average length of time to do training. Therefore the period over which the 1500 XP is earned may be shorter, meaning more XP/month, or longer, meaning less XP/month.
Let's do the math.
Take the maximum result on the training dice for the trainer's character class and divide 1500 by this number. For fighters, this would be 1500/4 years = 375 XP gained per year. For mages, this would be 1500/12 years = 125 XP gained per year. However, we want monthly figures, so we'll divide these results by 12, rounding as normal for counting numbers. For fighters this would be 375/12 = 31 (rounded down from 31.25). For mages this would be 125/12 = 10 (rounding down from 10.42). This final number is called the "base monthly gain."
Now we come to the training roll, the core of the process: after each month of training, the trainee rolls the training dice, MINUS the number of dice there are. (This is in order to sometimes produce a 0 result.) So trainee fighters would roll 1d4-1, and trainee mages would roll 2d6-2. The result is then multiplied by the base monthly gain, and the resulting product is the actual amount of XP the trainee earns that month.
Example 1: Frederick the trainee fighter rolls 1d4-1 after a month of training, and gets 3-1 = 2. He earns 31*2 or 62 XP for this month. Not bad!
Example 2: Molly the trainee mage rolls 2d6-2 after a month of training, and gets 2-2 = 0. She gains 0*10 = 0 XP this month. What a pity!
There must also be rules for total failure to learn, or "washing out." If any of the first 6 training rolls the trainee makes comes up with the minimum on the dice, then they must make a morale check. Failure means they have washed out: they are simply not cut out for this kind of training. A trainee who washes out keeps all the XP they've gained so far, except for the month they wash out; however, they cannot continue training in this particular character class.
A word about costs for materials and equipment: it's a placeholder, but at this time I'll simply say that training one trainee for one month requires a number of gold pieces equal to the average result of the training dice times the base monthly gain. For example, the cost to train a fighter trainee for one month is the average of 1d4-1, or 1.5, times the base monthly gain of 31 XP, for a monthly cost of 46.5 GP. One could expect the trainer to pass this cost on to the trainee as they see fit. I'm open to suggestions on this calculation, and it's absolutely not game-tested yet, nor does it fit in with my other economic calculations.
Let's step back and plot our course a little. There ought to be ways to earn bonuses for the training roll, thereby increasing the average XP the trainee earns, and negating the possibility of getting a 0 for the month's XP gain. There are also provisions to be made for determining how many trainees a single trainer can train at once. It would certainly make sense to be able to train another in a weapon proficiency. And obviously we'll need rules and training benefits for establishing a school, whether they take the form of a monk's dojo, a fighter's barracks, or a thief's underground den (at last, a concrete reason for a thieves' or assassins' guild to actually exist!)
All of these and more are the domain of the Instruction skill. I'll let any player character train someone into their class, but those with points in Instruction will be able to do it more efficiently, more quickly, or for more people. Here are a couple of the things I'm considering for the skill of Instruction (all subject to change, of course.)
The character is ignorant of methods of efficient instruction. They can only use the training rules as given above.
Multiple Trainees (20)
The instructor can train more than one person at once. They can train 1 trainee per 10 points of Instruction knowledge.
Establish School (50) (basic rules; more detailed ones will come later)
If the resources are available, the instructor can establish a school. The school must have at minimum its own living quarters and some kind of special area for instruction; depending on the type of school, this might be a sparring room, a lecture hall, or even a garden or wilderness area on a separate piece of land. Certain types of school may require additional facilities; for example, a school for training mages will require a laboratory and a library.
All trainees at a school will receive a +2 bonus on their training rolls each month. Furthermore, any instructor working at a school will enjoy a +3 bonus to the number of trainees they can personally train at one time, which of course stacks with the benefit of the Multiple Trainees knowledge.
Some types of schools can train more than one type of character class, as long as an appropriate instructor is available. For example, it's reasonable to allow an appropriately-staffed magical college to train both mages and illusionists.