If you want to keep them as techniques that I feel that they should be smaller things. I see them as minor magic items or similar to a mage book where the wizard is getting a few spells. The power may need to be similar. I shudder to think stackable or 'trees' to build on each other, but they could work as advanced techniques.
Some small things may be a free 5ft movement, maybe growing into 10ft teleport movement. Another minor thing may be +2 damage to undead or giants, or such.
Well if I went with feats, feats would represent advanced training in a school.
So, the White Lotus Adept feat might give the ability to move 5ft when an attack misses you, +1 Int, and maybe a stance that requires concentration and lets you add bonus damage to your melee weapon attacks with finesse weapons, or to your AC while wearing light or no armor and not using a shield, or something.
The Monk feat I proposed a while back might actually be a good school feat. Gaining a stance with the ability to reduce damage by 1d10+wisdom or intelligence+proficiency bonus as a reaction is pretty good. If you can counter attack as part of the same reaction if you reduce the damage to zero, even better. Perhaps the stance is a technique. You learn it, or one other stance technique if you already know it, when you take the feat, and gain the ability to counter attack with it.
Then, techniques would be stuff like this from Kobold Press, for flails, "
Shield Snare. As an action while wielding a flail, you may make a single attack roll against a target carrying a shield or a similar defensive tool. This attack ignores any bonus to AC granted by the shield and deals normal weapon damage. If the attack hits, the target must also make a Strength saving throw. On a failure, its shield is pulled from its grip and lands at its feet."
Hell, even if you could do it as a single attack, it wouldn't be more powerful than a common magic item, IMO.
I'd definitely lean towards making it more of a boon. "Training with a respected warrior to learn new techniques" should be the martial equivalent of "gathering reagents and casting spells to craft a magical item". Both should exist as narrative rewards outside of the character build economy.
I agree, and am considering making something like Rituals which are only gained via study in play, but can be learned by anyone trained in the right knowledge skill. Maybe tie it to tools, not sure yet, and there aren't as many tools that would make sense.
