There has been a fair consensus that certain schools are less useful that others.  Specifically Conjuration is more useful than necromancy, enchantment or evocation.  Part of this revision is moving less useful schools into combinations with more useful schools.  The other part is trying to bring some sense to how the schools interact with the world.  Currently the magic system is based on a hybrid aristotolean/mendelevian model which seems simultaneously to have the four element model and make a distinction between "real" and "unreal" elements.

The five schools work in exactly the same way as the 8 school model in terms of the rules but allow for some additional changes.  First each PC gets 2 ranks per level to spend on intelligence based skills over and above the standard skill allowance.  Second Spellcraft is split into five subschool corresponding to the new schools of magic.  This forces wizards either to put a large percentage of their skill points into being generalists studying all the schools of magic or lose access to knowledge skills in the breadth they usually have.

In addition there are some issues over things like how wizards school abilities work (basically Invokers use Evocation or some types of Conjuration, Incanters use Divination or Abjuration, Planomancers use Necromancy or Some forms of Conjuration, Transmogrifiers use Transmutation, Manipulators use Illusion or Enchantment).

Spells are moved into the five schools in a very particular order.  This is designed to allow any specific spell to be categorised.  Follow these steps one at a time to determine a spell's new school.

1) Any spell with the good, evil, law or chaos descriptor OR which is Conjuration (Calling) or Conjuration (Summoning) is a Planomancy spell (magic relating to the planes).

2) Any spell which does fire, force, sonic, acid, cold or electricity damage or which has a subtype related to those or which creates or manipulates inanimate materials (e.g. fog cloud) is an Invocation spell.

3) Any Illusion or Enchantment spell is a Manipulation spell.

4) Any spell with target "self" is a Transmogrification spell.  Any spell which changes the physical form is a Transmogrification spell.

5) Remaining necromancy spells are also Planomancy spells.

6) Remaining spells fall under Incantation spells.