Researchers have found that students in the United States display little interest in mathematics and science as early as the sixth grade. Multiple studies have established that elementary students' interest in these subjects is not only low but also decreases further throughout middle school and high school. Few studies have investigated students' interest in mathematics and science during the elementary years. Mathematics and science are essential subjects for future engineers and scientists, and the U.S. is experiencing a shortage in college students who are majoring in these fields. Understanding the attitudes of elementary students toward mathematics and science is essential to understanding the lack of interest students have in these subjects later in their education. This paper describes the development and the on-going validation of an assessment instrument that is designed to measure elementary student attitudes with respect to mathematics and science. Expert review and a factor analysis have been used in the development of the instrument, and subsequent results are reported. Additionally, this paper examines differences among elementary students' attitudes toward mathematics and science with respect to grade level and gender.