Many students in the United States are not proficient in mathematics. Mathematics vocabulary is one area that may impact students' understanding of and engagement with mathematics. This dissertation investigated the implementation, effectiveness, and teacher's perceptions of a program for teaching mathematics vocabulary necessary for fourth grade and beyond. This study randomly assigned 30 students (11-14 years old) to receive mathematics vocabulary instruction or not. Three teachers at a school for students with learning difficulties and disabilities administered mathematics vocabulary and mathematics achievement tests to all of their students before teaching the program to 17 of the students. A research assistant and I observed the teachers, and all of the teachers shared their perceptions of the lessons via a survey. Results show that the teachers taught the lessons as intended and that the students who received the lessons did better on the post-test than students who did not receive the lessons. Results from the survey suggest the teachers found the intervention acceptable, easy to use, and plan to use it or something similar to teach mathematics vocabulary in the future. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]