spell damage

[Drakkan]

In case some damaging spell is from two classes (fire / air) and I put skills in these magics, is damage increasing ? (means I can get 200% more damage at max ?)

[AsgarZigel]

Spells are always from only one school from what I can see, even if they require points in multiples. Fireball needs both Fire and Air, but is still a fire spell and levels up with Fire Magic.

The same with the ice spikes, which count as water magic despite needing 2 elements.