Specialization can be trained at level 20.
You need to train at least 1 point in each area of specialization to gain the ability.
The areas of specialization are: Abjuration, Alteration, Conjouration, Divination, Evocation
Only 1 specialization can rise above a skill of 50, and it will be the first one you get to 51, so be careful not to have Divination, Alteration, or Abjuration raise faster than Evo/Conj.
If you choose to specialize at or above level 50, you will exceed the specialization limit. You will need to reset your specialization with the Temple of Sol Ro quest
You can respecialize simply by doing this quest:
Give a Ruby to Ostorm in Temple of Sol Ro, and all your specializations will be reset to 49. Once you do this, memorize a low level spell in the area you wish to specialize in and cast it over and over until you see the specialization raise to 51.
11% mana reduction for 200 specialization
3% mana reduction for 50 specialization
Referencing the post on Spell Casting Mastery we see the following reductions in mana cost:
2.5% for SCM1
5% for SCM2
10% for SCM3
Specialization and Spell Casting Mastery stack linearly. So, for example, if you are casting a spell which you have 200 specialization for and you have SCM2, then you get 10 + 5 = 15% total mana reduction percentage.
If you have mana preservation items, these also further stack linearly, although items give random values within a range. For example, our 61+ focus earring gives a random reduction in mana cost from 1% to 15% on detrimental spells (nukes most generally).
Therefore, on detrimental spells, assuming you equip a summoned earring, have SCM 3, and Specialization 200 you would have the following mana savings:
11% + 10% + Random(1-15%) = Total Mana Reduction Percentage
Two schools of specialization exist for mages: Evocation and Conjuration. But which to pick?
This is an ageless debate, so I will only cover the main points.
Until high levels, all of our fire-based DDs, as well as all rains, bolts, PBAEs, and anti-summon DDs are Evocation based. Only our Shock nukes (including Shock of Fiery Blades and Sun Vortex) are Conjuration based.
However, the vast majority of our spells, including all pet summons, are Conjuration based. Additionally our higher level pet heals are Conjuration based as well
Ultimately you should specialize in which ever type of spell you cast the most. If you mostly use Evocation spells, then specialize Evocation. Likewise if you use mostly Conjuration spells then you should specialize Conjuration.
The predominant trend is: Specialize Evocation at level 20, and switch to Conjuration some time during the mid 50s. The majority of level 65 magicians are specialized in Conjuration, while the rest are Evocation.
Thanks to Suzanna Dreamingheart for compiling the original impetus for this post