Mathematical dyscalculia (MD) is a neurodevelopmental difficulty that compromises number sense, arithmetic fluency, and quantitative reasoning, constraining mastery-based progression within Kenya’s competency-based education (CBE) and undermining performance in mathematics and numeracy-intensive subjects such as science, economics, and technology. This systematic review synthesizes evidence on MD’s academic impact among senior school learners (14–18 years) in Kenyan public schools under CBE, focusing on awareness, diagnostic capacity, inclusive strategies, and teacher training. A PRISMA-aligned search covering 10 years was conducted across electronic databases, supplemented by reference and gray literature screening. Studies were independently screened, data were extracted using standardized forms, and methodological quality was appraised using the CASP. Given the study heterogeneity, the findings were narratively synthesized with descriptive summaries. The review identified significant system-readiness gaps: over 70% of schools lacked formal MD screening, while under 40% of senior teachers received training to identify or accommodate learners with MD. These deficiencies contributed to the delayed identification and inconsistent implementation of support, including multisensory instruction, personalized plans, visual aids, tutoring, and assistive technologies, especially in rural settings.