Are there any rules (house or otherwise) for increasing ability scores after character creation in Basic D&D or any of its retro clones? (Other than magic items or wishes.)
When we generated ability scores, the players rolled 3d6 in order to create their characters. Now that they have a little experience under their belts, they are looking for ways to increase things like Strength for to-hit and damage bonuses, Dexterity to add to AC/Init, and Charisma to add to reaction checks.
Best Answer
BX doesn't put the same weight on the ability scores as you appear to, so beware that adding an ability score advancement mechanic will redirect some of your players motivations away from looking for harder-to-achieve bonuses to their effectiveness. On the other hand, you don't have to worry much about breaking the balance of the game with this, because BFRPG is not a tightly-balanced game to begin with – you'll just end up seeing them tackle slightly more challenging fights than you would otherwise. With that caveat out of the way, voiding the warranty on your game can be done for fun an profit! Open up that case, change some internal workings, and see how the machine ticks differently…
I've done some informed searching and turned up a few suggestions and play tested methods for how to do this. Due to the nature of online materials generated by the Old School Renaissance, much of this is musings about possible house rules and only some are house rules groups have actually used and seen the effects of. But experimenting is one of the great things about a simple base system like Basic Fantasy RPG or BX D&D, so have at it!
One option I saw mentioned in passing (but not explained, so there was nothing to quote, and therefore this is my own development of the suggestion) is to use the ability score advancement rules from AD&D's Unearthed Arcana, as found on page 15. AD&D isn't BX of course, but they're largely intercompatible in terms of rules so there's no conflict there, and the fact that the games have different assumptions about advancement and such is irrelevant since you're already going off the beaten track.
The essential idea, if you don't have access to UA, is that each ability score that's core to the class has 100 sub-points, so your DEX would be 15/32, for example, meaning 15 DEX with 35/100 points of advancement toward having DEX 16. Each level you roll 2d10 for each primary score and add that to the percentile part; when you hit 100 you increase the stat by 1 and reset the percentile to 1/100 (discarding extra points rolled over 100).
Something similar to the UA scheme is from the post “Hacking Hackmaster Part 3 (on Fractional Ability Points)”, but heavily modified to account for different classes and to allow for progressing in all ability scores. (And, obviously, it came to the author via Hackmaster, which itself took the idea from the original Unearthed Arcana.) It's the one I like the most too, because it gives you the ability to increase ability scores without making it overpowered, while also giving your players the excitement of seeing those numbers climb toward 100. The advantage of this over the UA method is that it's well-tuned to multiple classes, while the UA method was originally just designed for the Cavalier AD&D class.
The details for each class can be found in that post, but the gist of it is that you have 6 polyhedral dice — d20, d12, d10, d8, d6, d4 — and six ability scores. Each class advances their fractional ability score number by the amount rolled on a die that corresponds to how core that stat is to the class. For example, the table shows fighters getting +1d20 to fractional Strength but only +1d6 to fractional Wisdom at level-up; meanwhile Clerics get +1d20 fractional Wisdom and +1d4 fractional Dexterity at level-up.
The post “Normalising ability scores and ability checks in D&D” proposes (i.e., it's untested) that stats be rolled on 2d6+3 instead of 3d6, in order to raise the minimum and make higher stats more likely, but the bit of the post that's more relevant to your needs is the suggestion to allow +1 to one ability score every level, with a hard 18 cap. The author's guiding light is the idea that, back in the early days of D&D, he figures everyone fudged their dice rolls anyway in order to get high scores, so why not fix the ability score rules so that it happens naturally without cheating? There are some other variants suggested for how to advance scores, but they all amount to slowing down the +1 by making it every few levels.
The post “‘Landmark’ Levels” suggests that the primary ability score gets +1 at some fixed level breakpoints, such as 5/10/15. This is a nice and simple rule that gives a way to advance, but doesn't much increase the power level over standard BX or BFRPG.
It's a common house rule during character generation to be allowed to bump one low stat by 1 point by lowering another one by 2 points, subject to limits (such as only lowering scores that are higher than the raised score). If you're looking to fix your players' scores instead of adding ongoing advancement to the game, you might consider retroactively allowing them to adjust their scores this way.
This is a real-not-house rule in the B/X retroclone Adventurer Conqueror King System (ACKS), but with the further limit that the increased stat must be a core/requisite class score, lowered scores must not be core scores, that no stat may be lowered below 8, and the 2 points of reduction can't be split across different stats.
You can also just use standard D&D 3.x advancement, maybe with per-class restrictions (such as only being able to advance your class's core stat). D&D 3 lets you pick a stat to advance every X levels (depending on class). Since BFRPG is based on the 3rd edition SRD, this is an easy house rule to directly port over.