To determine the effectiveness of mathematical vocabulary training on the problem solving ability of third and fourth grade students, 66 students were placed into either an experimental or a control group. All were pretested and posttested with an experimental mathematics vocabulary test and with a standardized mathematics test. Mathematical vocabulary was then taught to the experimental group for eight weeks. The results favored the experimental group. There were significant differences between the gain scores of the two groups on both the vocabulary test and on the standardized test. The findings suggest that systematic mathematical vocabulary training increased the problem solving ability of third and fourth grade students. (Author/FL)