This study aimed to determine the effect of localized lesson plans to the interest and performance in mathematics. The respondents were grade 6 pupils of Odiong Elementary School, Philippines in the school year 2019-2020. The experimental grouped was exposed to instruction using localized lesson plans while the control grouped was exposed to ready-made lesson plans. The results showed that the pupils' level of interests before and after using localized and ready-made lesson are both highly interested; level of performance before using localized was fairly satisfactory, and after using it show it was very satisfactory. Moreover, there is a significant difference between the pupils' interest and academic performance after using localized lesson plans. It indicates that pupils' performance in mathematics under localized lesson plans instruction is much higher than pupils' under ready-made lesson plans instruction. Thus, it is recommended to use localized lesson plans in teaching any subject.