Children learning to write often reverse individual letters 180̊ about their horizontal axis so that they become legible when viewed in a mirror. This phenomenon is common amongst the 4-7 year old age group. Previous research demonstrated inconsistent results regarding the relationship between mirror-errors and perceptual confusion of left and right. Only one study examined mirror-writing in preschool children asked to write with both hands and reported a higher incidence of mirror-writing with the left hand. The present study investigated the relationship between perceptual errors in letter directionality and mirror-reversals of individual letters using a digitizing-tablet. Our results show a strong correlation between perceptual-errors and mirror-errors and support the spatial-orientation explanations of mirror-writing, which suggest that mirror-errors are produced as a result of perceptual uncertainty about the directionality of letters. Furthermore, the data support the implicit right-writing rule and show that two left-facing characters “J” and “Z” were by far most frequently mirror-reversed. All children were asked to write with their preferred and non-preferred hand and only children older than 75.5 months were found to produce more reversal errors when writing with their non-preferred hand. This result is in line with the motor explanation of mirror-writing, in the way that children for whom the direction of letters is accrued knowledge make more mirror-errors with their non-preferred hand.