OBJECTIVE To investigate the contribution of stimulus and response differences to the different developmental courses of grating and optotype visual acuity at the preschool age range. METHODS Binocular visual acuity at 228 cm was assessed in 205 children in 7 age groups between 2.5 and 6 years and in 12 adults. Acuities were obtained in three tasks: detection of a grating in one of two positions, discrimination of the orientation of a single grating, and discrimination of the orientation of the gap in an uncrowded Landolt-C optotype. The three paradigms were as similar as possible in stimulus contrast, luminance, presentation mode, and psychophysical procedure. RESULTS Mean grating and optotype acuities were lower than adult acuities at all ages. Optotype acuity was overall higher and increased faster with age than grating acuities. Grating orientation acuity was slightly but not significantly lower than grating detection acuity in all but one age group. The grating detection task was successful at earlier ages (100% at 3.5 years) than both the optotype acuity task (100% at 4.5 years) and the grating orientation task (100% at 5.75 years). CONCLUSIONS Optotype and grating acuities follow a different developmental course in children between 3 and 6 years of age, with optotype acuity growing superior to grating acuity in that age range. The similarity of grating orientation to grating detection acuities and the difference between grating and optotype acuities suggest that superior optotype acuity is due to stimulus characteristics rather than to the complexity of the response required.