Throughout the world, mathematical competence is necessary for personal fulfillment, active citizenship, social inclusion and employability. Education stakeholders in many countries have expressed increasing concern about achievement in mathematics. Language plays a significant role in mathematical solution to various tasks and may affect achievement. A learner may not perform well in mathematics not necessarily because of weak mathematical ability but due to challenges in understanding the language involved. The purpose of the study was to explore the effects of language-based factors in the assessment tasks on student achievement in mathematics. The study employed descriptive survey research design. The research was carried out in ten secondary schools in Tharaka-Nithi County, Kenya. The subjects were form four students and simple random sampling technique was used to select the participating schools. Mathematics Achievement Tests were administered to provide the needed data. Descriptive statistics were used to analyse the data obtained. Results of the study revealed that solving mathematical problems modified into mathematical expressions had a positive effect on improving student mathematics achievement. The findings gives insights to test developers to provide effective assessment that incorporates a variety of approaches that recognize the strengths of students especially those struggling with English language.
Key words: Language issues, Achievement, Mathematical word problems.