Calculator usage in the United States is prevalent in secondary education classrooms. There has been a decline in mathematics achievement in national and international assessments for U.S. students. The U.S. historically introduces the calculator in mathematics classrooms earlier than several other countries, including: Singapore, Ireland, South Korea, Czech Republic, Austria and the Netherlands. This mixed methods study researches the potential impact of early calculator usage and fundamental mathematics skills in two ways: 1) a quantitative proctored mathematics assessment administered to middle and high school students, without access to calculators 2) qualitative semi-structured interviews from teachers to determine perceptions on student fundamental mathematics skills. Both the qualitative and the quantitative strands analyze the observations and insights on calculator usage in the classroom to determine student fundamental mathematics skills (FMS). The hypothesis for the study presumes there is no significant difference between 8th and 12th graders' scores on a fundamental mathematics skills assessment (FMSA), when assessed without the use of a calculator. However, this study shows that there is indeed a statistically significant difference between the two groups; the middle school 8th grade students had higher scores than the 12th graders on the (FMSA), as assessed without a calculator. Moreover, students believe they need calculators and teachers permit calculator usage, often without restriction (including exams), although teachers acknowledge limited FMS of students, without a calculator. Teachers believe that FMS should be attained before 8th grade. Without a firm foundation in the mastery of basic skills, it is difficult for students to move to higher levels of mathematics understanding. As a result, future research efforts will look at the elementary school level to see how far the early calculator usage extends and encompass comparison between elementary and middle. [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://www.proquest.com/en-US/products/dissertations/individuals.shtml.]