This study investigates Lesson Plan Development and Teaching Mathematics in Kisoro District with a focus on Kasoni Primary School. Using a sample size of 80 respondents, which included 40 students, 30 parents, 8 teachers, and 1 district education officer, the research aimed to achieve three key objectives: (1) to assess the extent of lesson plan development at Kasoni Primary School, (2) to evaluate the level of mathematics teaching at the school, and (3) to establish the relationship between lesson plan development and the teaching of mathematics. The study adopted a descriptive research design and utilized data collection methods such as questionnaires, interviews, and document reviews. Findings revealed that lesson planning was conducted to varying degrees, but challenges such as limited instructional resources and inconsistent monitoring hindered optimal implementation. The study also found that teaching mathematics at Kasoni Primary School exhibited significant gaps, including a lack of learner-centered approaches and minimal use of teaching aids. A strong positive relationship was identified between effective lesson plan development and enhanced teaching outcomes in mathematics. The study concludes that lesson plan development plays a crucial role in improving the teaching of mathematics. Recommendations include providing teachers with ongoing professional development in lesson planning, increasing access to teaching resources, and strengthening the supervision of lesson plan implementation. Further research is suggested to examine similar issues in other schools and districts to build on these findings.