Umm... I'll assume you know what a healing spell is. Classes well known for healing are Druids, Clerics, Shaman and Healers. Heal spells in the base tracks have variance, like DD's. However, heal spells in the specialization tracks have no variance, no matter what your training is. If you have the spell, you will heal for 125% of the Delve value, all the time.

Is there anything else I should know about training in spell skills?
Actually, now that you mention it, the more you Specialize in a spell skill, the better and more effective spells from that school of magic will become, both the Base Track spells and the Mastery Track spells.

In other words, spell training decreases the numerical variance for your spells. A few spell numbers are not affected this way, however, for things such as healing lines in the specialization track, and anything with a time value. Suppose you are a wizard, and you have a fire nuke capable of doing 200 damage. With full training in Path of Fire your wizard will do 200 damage almost every time to an even-con monster (ignoring resists), while a wizard with no training in Path of Fire might just get a random damage number from 100 to 200.

If you are a healing class, the heal spells in your base lines have variance, but the heal spells in the specialization lines will always heal the same amount of hit points each time.