The purpose of this retrospective study was to describe the magnitude, nature, and costs of assault injuries among teachers, a high-risk group. Review of assault cases (N = 341) was based on internal and case management vendor records. The 3-year assault rate was 3.24 per 1,000 teachers. Assaults were predominately physical, occurring during classroom disputes and while restraining students. Assaults accounted for 2,480 lost workdays and more than dollars 714,000 in lost wages and case management fees. The most costly injuries on a per-case basis were strain-sprain injuries resulting in lost workdays and fractures not resulting in lost workdays. Less than 20% of the assaults accounted for all of the lost workdays and most of the case costs. Study variables accounted for 13% of case costs. Occupational health nurses should collaborate with school personnel, administrators, and parents to develop prevention programs, which may include de-escalation techniques for teachers as well as case management strategies.