Scaling Spells

A scaling spell is one that can be learned at different levels of difficulty for enhanced, or sometimes, decreased effect.
The level of which the spell is cast determines which version of the spell is. For instance, a normal fireball spell is a third level spell. If fireball were converted to a scaling spell, fireball III would be the basic spell, with fireball II being a 2nd level weaker version of the standard spell.
Learning a higher level version of a spell has the same requirements for learning any other spell. The only difference is all the lower level versions of the spell are worked in so that if you learn version VII of a spell, you now also know all versions VI and below. And these extra spells versions don't count toward your max number of spells known.
Priests also have access to scaling spells, however, their deity may only grant scaling spells to a particular level.
Meta-magic feats can be combined with any scaling spell. A memorized scaling spell takes up the appropriate spell slot for its level for which it is memorized. However, the caster can choose to cast the spell at a lower version at any time. For instance, memorizing fireball V would require a 5th level slot to be used. However, at the time of casting, the caster could choose to cast it as a lower version.
Additionally, some scaling spells can have their effects combined. For instance, if there is a mark 2 and mark 4 version, the caster can cast it as a 6th level spell to gain both versions. The individual spell will notate if this is possible.
Not all scaling spells have a version for each level.