In Skyrim when you play as mage character you can dualcast spells to do 2x effects. Does this affect leveling that skill too?
According to a couple of my personal tests, inserting a delay between the lmb and rmb presses, and casting the spell as if without the dual casting perk - twice, results in the fastest leveling. Twice as fast, more or less.
Also, it appears that the higher level the spell, the faster is the leveling process.