Possible Clues:

• Describing one who was his own master?
• Not educated by others
• Like many musicians (2 words)
• To learn by oneself is to be this (hyph.)
• It's no thanks to teachers I can read and write having trained in solitary confinement?
• Unruly thug Alf in class of limited ability may be this
• Learned without help
• Nobody else instructed one to be this
• Proficient through one's own methods
• The fat slug (anag) (4-6)