Magic or Education?

I took both of these skill lines, keeping in mind that many already have Summoning taking up a slot (if mentors are available, switch to Chaos), and we also definitely take Darkness. And the last skill line is most often Logistics or Offense due to Ranged Attack.

A Necromancer without defense won't last long. He'll fall apart before he has time to cast spells, and the damage from basic attacks is high. Summoning is more reliable, and there's rarely a need to switch it to Chaos. Offense is good for Necromancers, but it's taken primarily for Battle Battle and Speed.