A study investigated the effectiveness of an intervention for improving adolescent writing and speaking using mathematical language. The targeted population consists of high school students in a growing, middle- and upper-middle-class, suburban community located west of Chicago, Illinois. The problems of writing and speaking using mathematical language have been documented by data collected from teacher observations, student interviews, and teacher-made assessments. Analysis of probable cause data reveals that students lack the basic understanding of math vocabulary, lack confidence in their math abilities, and lack the knowledge of math writing skills. Reviews of curricular content and previous instructional methods reveal an over-emphasis on basic skills and computation with minimal attention to writing and speaking using mathematical language. Solution strategies suggested by knowledgeable others, combined with an analysis of the problem setting has resulted in a selection of one major intervention--an increase of instructional emphasis on writing and speaking using mathematical language through the use of journal writing, cooperative learning, and portfolio assessment. Results indicated that: (1) students' attitudes toward writing and mathematics improved; (2) students' understanding of mathematics improved; and (3) students showed an increase in their ability to talk mathematically. Contains 34 references and 7 tables of data. Appendixes present survey instruments, interview questions, sample journal questions, a sample social skills lesson plan, sample test questions, and group self-evaluations. (Author/RS)