Purpose. To evaluate the ability of children to perform computer-based matching and to evaluate the accuracy and reliability of size lens induced aniseikonia measurement using the Aniseikonia Inspector version 1. Methods. Fifty-seven children in grades 1, 3, and 5 (aged 6 to 11 years) completed four trials per each of four conditions: control (associated binocular), dissociated (wearing red/green filters only), and dissociated with 3.5% afocal (size) lens over the right eye and size lens over the left eye (the latter two conditions in predetermined random order). Children adjusted the size of a variable semicircle seen by one eye in 0.5% steps using computer arrow keys to match the size of a nonvariable semicircle seen by the other eye. Testing was performed in the dark using large targets oriented vertically. Results. The repeatability coefficient (sw), based on individual measures, was lowest for the control condition. Repeated measures (mean of four trials) show that adjustments with red/green dissociation only were not significantly different from zero size difference, with narrow confidence limit widths at all ages (0.54, 0.42, and 0.22% at grades 1, 3, and 5, respectively). Repeated measures of induced aniseikonia showed increased confidence limit widths (width for right eye condition was 2.77, 0.71, and 0.82% at grades 1, 3, and 5, respectively). Measured aniseikonia (mean of four adjustments) was less than induced aniseikonia with slopes of regressions lines insignificantly <1.0 for all grades. Conclusions. Children as young as 6 years are capable of making the adjustments necessary to obtain a measure of aniseikonia under dissociated conditions with sufficient accuracy and reliability to be clinically useful using the Aniseikonia Inspector software (version 1 with large targets in the dark). Further study is necessary to show how children with natural aniseikonia respond to testing. © Copyright 2010 American Academy of Optometry.