Background: The back saver sit and reach (BSSR) test is probably the most frequently quantitative tool used to estimate hamstring flexibility in the school and physical-sporting field due to its simplicity and quickly implementation. However, there is limited scientific evidence to justify its use in colombian girls. Objective: To assess the validity and intra-rater reliability of the BSSR in girls of a school from Bucaramanga. Mathodology: A study of evaluation of diagnostic technology was done in 64 girls (7-8 years), selected by convenience. BSSR test and straight leg raising test (SLRT) were conducted on two consecutive occasions by the same researchers. It was calculed the Pearson (r) or intraclass (ICC) correlation coefficient with their respective confidence intervals (95% CI 95%). Results: The global validity was good (r=0.61 (95% CI 0.43-0.75) – r=0.66 (95% CI 0.49-0.78)), while intra-rater reliability was very good in the left lower limb [ICC= 0.90 (95% CI 0.67 to 0.96)] and right lower limb [ICC = 0.88 (95% CI 0.63 to 0.95)]. Conclusion: BSSR test has good reliability and validity for assessing lower limb flexibility in girls aged 7 to 8 years.