When does a character need a mentor?

As your characters gain levels, you will notice that I sometimes do, and sometimes don't require training for skills and feats. This training requirement is somewhat judgment based, but isn't entirely arbitrary. In general, I'm following the rules outlined below.

Gaining Levels:

• •Advancing as current character class - don't need a mentor. However, certain skills, feats, spells and sociopolitical advancements require mentorship, guild membership or a quest. This is covered in more detail in the Gaining Levels article.
• •New character class - either need a mentor or a reference in the character's background indicating previous training or tendency towards another class. You typically learn enough during a month of training to be eligible for the new character class. My world doesn't require an XP penalty for multi-classing, which I see as nothing more than a game mechanic.
• •School specialization - need a mentor. You typically learn enough during a month of training to be eligible for the new character class.
• •Prestige class - character must make minimum level requirement, needs a mentor, learns enough during a month of training to be eligible for the new character class but must pass a test or quest to be eligible for advancement.

Skills:

• •Untrained class skill - don't need a mentor. You can take these points whenever you gain a level.
• •Trained class skill - need a mentor or formal training once every few levels. You typically learn enough during a month of training to last three levels worth of skill advancement.
• •Untrained cross-class skill - generally don't need a mentor. The cross-class penalty reflects the lack of proper training.
• •Trained cross-class skill - requires considerable mentorship. You typically learn enough during a month of training to last one level worth of skill advancement.
• •Exclusive skill - requires both proper character class and a mentor or formal training once every few levels. You typically learn enough during a month of training to last three levels worth of skill advancement.

Feats:

• •Most feats require no mentorship; level advancement is adequate.

However, the few feats requiring mentorship are often esoteric feats that the character may never have seen performed, so are only available at high level. The character typically has to meet prerequisites, and then train for a month to be eligible. These include:

• •Track (rangers get this automatically)
• •Spring Attack
• •Whirlwind Attack
• •Improved Critical
• •Stunning Fist (monks get this at the appropriate level)
• •Weapon Specialization
• •Spirited Charge
• •Extra Turning

The following feats require either mentorship or independent study:

• •All Item Creation feats
• •Spell Mastery