The study of the age trend development of different physical abilities in childhood and adolescence are one of the important areas in physical education. The study was conducted to investigate the rate and magnitude of age- associated changes of power and flexibility in 10 to 14 years old school going boys. For this purpose a total of 500 school-going boys were selected randomly from different schools of CoochBehar. The age of the boys was from 10 years to 14 years. Power was measured by standing broad jump test and flexibility was assessed by using Jonson box. Multiple group design with five independent groups (G1, G2, G3, G4 and G5) was formed for the present study and each age group had 100 boys within it. Mean value and standard deviation were computed for each parameter as descriptive statistics. To find out the inter group difference in power and flexibility, analysis of variance (ANOVA) was used in this study. Significance level set for the study was only 0.05 level of confidence. Results revealed that power and flexibility increased linearly across all of the age groups from 10 to 14 years. Peak velocity of improvement for the power and flexibility were found for G3 -G4 age group and G4 – G5 age groups respectively.