In short: Specialist mages have become narrowly trained in a specific field of magic. Specialists receive one additional spell per spell level than unspecialized mages. Because of their specialization, these mages receive a +15% chance to learn spells from their school but suffer a -15% penalty when learning spells outside their specialty. When saving against spells within his chosen school, the specialist receives a +1 to saving throws.
Similarly, the specialist's enemies suffer a -1 penalty when saving against spells cast by the specialist within his field. Specialists are unable to cast spells from the opposing school. Mages must be single-classed or dual-classed to specialize with the exception of gnomes. Gnomes can only be illusionists so are permitted to multiclass. A specialist must have a 9 intelligence in addition to the School-specific minimum ability. The prime requisites for specialty mages are intelligence and their School's ability.

Requirements: Race: Human/Half-Elf, Dexterity: 15

School: Alteration

Opposition School: Abjuration, Necromancy

School Description: Alteration spells cause a change in the properties of some already existing thing, creature, or condition. This is accomplished by magical energy channeled through the wizard.

Alteration spells in the original Baldur's Gate (with the Tales of the Sword Coast addon installed): Burning Hands, Colour Spray, Shocking Grasp, Knock, Strength, Vocalise, Haste, Slow, Dimension Door, Otiluke's Resilient Sphere, Polymorph Other and Polymorph Self.