This book highlights the importance of reform-based curriculum in mathematics and gives the readers valuable and critical information about the implementation of a theory based mathematics curriculum in teaching and its positive influence on students'' achievement and motivation in geometry. There is a chapter that talks about the problems regarding the failure of students in geometry, and offers a solution for both mathematics teachers and students to overcome the problems faced in the classrooms. The author gives the readers detail information about the van Hiele theory, its instructional phases and the research done on this theory in the following chapter. Furthermore, in this chapter the author examines the research studies done on students'' performance and motivation in mathematics, highlights the gender issues in learning geometry and introduces several standard-based mathematics curricula and their effects on the students'' achievement in mathematics. At the end of the book, the author shows and discusses the great influences of the reform-based curricula on the students'' performance and motivation in geometry.