Does "Summon Arniel's Shade" Level Conjuration Skill?

I've been using "Summon Arniel's Shade" a lot, usually right when I'm first aware of an enemy, often even to lure enemies out. But my conjuration skill doesn't seem to be leveling fast: it's at about 74-75. I think it's only leveling when I cast Soul Trap, Bound Weapon, or Summon Atronach spells.

Is this because XP is tied to base cost and Arniel's Shade costs 0 magica? Or is it because I have to start a fight first, then cast the spell?

Normally, you get experience everytime you summon something. The higher levels your spells are (e.g. a master spell), the more xp you will gain. BUT you're right, you need to be in a battle, in order to get the experience.

I think when using novice spells you get only a small amount of xp, that you won't even notice on the experience bar.

My tip: summon the highest level creatures, fight them and repeat. That's how I level up my conjuration skill.

For more detailed information about conjuration xp, check out this article or this talk page.