This study aims at evaluating the effect on dental caries of acidulated phosphate fluoride gel applied topically with different concentrations (1.23% versus 0.4%), frequencies (once a year versus twice a year versus four times a year), and times of application (4 minutes versus 1 minute) and investigates the scope of topical APF gel effect on initial carious lesions as well as on newly erupted teeth. A sample of (340) school children (177 males and 163 females) initially in the fourth grade (aged 9-11 years) were collected from (4) primary schools in Mosul City Centre. The children were allocated randomly to five experimental groups and one control group. The dental examinations were done using DMFT and DMFS indices: one before fluoride application and the other after one year. The results reveal that the use of such a fluoride therapy as a school-based programme is advised for all children with evidence of dental caries, and is recommended to be planned to match the pattern of eruption of teeth.