I'm playing my pure mage right now, Breton, with the Mage stone [I usually keep it until they pass the beginner levels]

Is it just my imagination, but compared to my spell assassin, the mages level slow?

WTF! Why is my pure mage leveling so so slow?

It depends how much magic you use.

For instance, my latest spellsword was going straight for Dragons Rising and reached it at level 11, which is pretty high for me.

Exemple: If you cast Oakflesh, summon a Familiar, use Spark on bandits and finish them off with a sword, then use a bit of resto to heal, you'll level pretty fast.

If you just go in and spam firebolts, then yes, it will be slower.

My is usually:

-Conjure Atronauch

-Oakflesh

-Fireball

-Flee if I get in a pickle

-Repeat

Depends on the school of magic. As Arverne pointed out, Destruction levels slower than some of the other schools because it only levels when it's used against an enemy. Most of the other schools have at least one spell that you can use on yourself: Illusion (Muffle), Alteration (the flesh spells, magelight, candlelight), Conjuration (casting an atronach gives you credit, but very little; still, it's something), Restoration (healing). You don't even have to spam them, just use them normally, but they'll still level faster than Destruction.

Well that really svcks because I'm a conjurer and my main combat damage is reliant on destruction.

When it comes to magic and especially, destruction and restoration* (the two hardest to level of all) the higher the cost, the higher the xp gain. In the case of destruction, Flames aren't going to cut it after a short while -you'll have to move to the next tier of spells and so goes.

Illusion and Conjuration are easy to level. Alteration seems to level a a good pace as long as you're using your flesh spells for battle.

Destruction and Restoration are more tricky. This is where trainers come in to play. Use them.