The fundamental importance of basic mathematics to daily life is emphasized in this teacher's guide for special education teachers in Puerto Rico. While it is necessary for the teacher to determine the needs and abilities of each student and adapt the curriculum accordingly, this guide presents, in Spanish, a set of lesson plans, each with an objective and suggested activities toward the objective. Activities are chosen for their practical relevance. Skills are presented in the following areas: (1) numeration, including cardinal, ordinal, and Roman numerals; (2) basic mathematics operations, including fractions and decimals; (3) measurement of time, temperature, volume, weight in the English and metric systems, and the monetary system; and (4) principles of geometry. An appendix provides specific guidance in teaching basic mathematical operations. (Contains 12 references.) (SLD)