Skyrim talk:Fortify Conjuration
While the page is perfectly clear about the spell cost decreasing, it may be helpful to point out that the skill itself, as it appears in the skills sub-menu, does not increase (turn green) as a result of Fortify Conjuration as it does for the fortification of some other skills. This reduced spell cost benefit seems to be applied to all skills that burn magicka, rather than applying the fortification benefit directly to the skill per se. My confusion arose for a character at Conjuration skill level 100 when he donned a Fortify Conjuration 15% armor in order to conjure a Thrall. It didn't work and there was no green on the skills menu. However, I later confirmed that the armor actually reduced the cost as advertised by looking at the difference in spell costs, but 15% just wasn't enough without the Master perk. So I appended:
"In enchantments, Fortify Conjuration decreases the cost of Conjuration spells, and the use cost of Conjuration based enchantments. It does not increase the skill level for Conjuration which appears in the skills sub-menu."