The Daily Mile is a promising initiative aimed at removing some of the barriers to physical activity in the school setting. This quasi-experimental study investigated the dose–effect of The Daily Mile on cardiorespiratory fitness, waist-to-height ratio, and body mass index (BMI) after a period of 3- and 6-months. A total of 279 students (mean age = 9 ± 1 years) participated in The Daily Mile while 269 students (mean age = 9 ± 1 years) did not (control group). A posteriori, the classes performing The Daily Mile on average two times per week were included in the 2_times subgroup, while those performing the activity on average three times per week in the 3_times subgroup. A significant difference was observed in favor of the experimental compared to the control group in the 6 Minute Run Test (F = 13.932, p = 0.008). Moreover, the improvement of the 6-minute run test was more pronounced for 3_times (effect size = 0.51) rather than for the 2_times subgroup (effect size = 0.29). No differences were observed in waist-to-height ratio and BMI scores. In conclusion, teachers are strongly recommended to implement The Daily Mile at least three times a week to see appreciable effects on cardiorespiratory fitness.