The original Twilight 2000 had something very similar to what BRP uses. It's been a really long time since I played that system so the details are foggy. I recall putting a mark by skills when I failed. Then at a GM determined time (after the adventure) any skill had some sort of roll to see if the character did improve the skill. I think it was another roll against the same skill and you wanted to roll above the skill (d100 just like BRP). Then depending on the scope of the failure there was a minor plus to the skill. Maybe an upgrade of 1d6. It worked well enough. Easy enough for the table to rule out silly skill improvement strategies like shooting rats in a pit to improve gun skills as that isn't the flavor of game we wanted. Enough of a reason to try to something risky in game at times even if we were not good at it yet. Nice and simple bookkeeping.
In Burning Wheel to raise a skill the test needs to be a mix of several tests across a few categories of difficulty. If memory serve it was something like try test "Routine, Challenging and Difficult" challenge rating. The higher the skill, the more Challenging and Difficult tests were needed. A higher skill also meant it was harder to create/find Challenging and Difficult tests as well (e.g. low level negotiation with a small town police squad to let you go for petty theft vs. high level convincing a dragon you were just borrowing their entire treasure horde for the 2nd time). Through the mechanics it even gave players reasons to ask others not to help to keep the test difficult enough. It did require quite a bit of bookkeeping for the players. BW also breaks out rules for practice vs. training vs. skill improvement as different things which addresses some of the skill improvement system abuse raised as a concern. The details are in the free BW Hub document if you are interested.
In Burning Wheel to raise a skill the test needs to be a mix of several tests across a few categories of difficulty. If memory serve it was something like try test "Routine, Challenging and Difficult" challenge rating. The higher the skill, the more Challenging and Difficult tests were needed. A higher skill also meant it was harder to create/find Challenging and Difficult tests as well (e.g. low level negotiation with a small town police squad to let you go for petty theft vs. high level convincing a dragon you were just borrowing their entire treasure horde for the 2nd time). Through the mechanics it even gave players reasons to ask others not to help to keep the test difficult enough. It did require quite a bit of bookkeeping for the players. BW also breaks out rules for practice vs. training vs. skill improvement as different things which addresses some of the skill improvement system abuse raised as a concern. The details are in the free BW Hub document if you are interested.
