Agricultural mechanics laboratory management skills are essential for school-based agriculture teachers who instruct students in an agricultural mechanics laboratory (Bear & Hoerner, 1986). McKim and Saucier (2011) suggested the frequency and severity of accidents that occur in these laboratories can be reduced when these facilities are managed by educators who are competent and knowledgeable in the area of laboratory safety and facility management. This study investigated changes in Missouri agriculture teachers' perceived agricultural mechanics laboratory management competency from 1989 to 2008, percent changes between 1989 and 2008 and effect size were used to describe changes in importance and ability of the selected competencies. Results indicated that teachers in 2008 had more teaching experience than their predecessors, less university semester credit hours of agricultural mechanics instruction, taught courses with greater student enrollment in laboratories that had less working space per student. Further, teachers' perceptions of the importance of agricultural mechanics laboratory management competencies had a negligible change. However, the changes in teachers' perceived ability to perform development, writing, and planning competencies were notable.