With the aim of "intimidating pupils and disrupting learning." This will do it, all right. From [1] MSNBC, with thanks to CM:

BAGHDAD, Iraq - Separate groups of gunmen entered two primary schools in Baghdad on Wednesday and beheaded two teachers in front of their students, the Ministry of State for National Security said.

"Two terrorist groups beheaded two teachers in front of their students in the Amna and Shaheed Hamdi primary schools in Shaab district in Baghdad," a ministry statement said.

A ministry official said he believed the attacks were aimed at "intimidating pupils and disrupting learning."

UPDATE: [2] This story appears to be inaccurate. (Thanks to Matt.)