The focus of this book is an investigation of the effects of Cooperative Learning on mathematics achievements and attitudes of secondary school students. The study was carried out in Kakamega district, located in the western region of Kenya, Africa. Although mathematics is essential for career development and it provides a solid foundation for many aspects of daily life, Kenya Certificate of Secondary Examination (KCSE) candidates persistently perform poorly in mathematics as compared to the other subjects offered. KCSE is a national examination that should be taken by all secondary school students at the end of the four year cycle. Each candidate sits for examinations in at least seven subjects. Mathematics is one of the core subjects to be examined. Section one of each of the two papers which candidates sit for tests basic mathematical skills. However, many candidates score zero in K.C.S.E. mathematics. The poor performance in mathematics is a growing concern among parents, teachers and other stakeholders.