In this article, time effects on intelligence test scores have been investigated. In particular, we examined whether the "Flynn effect" is manifest in children from the middle and higher IQ distribution range, measured with a child intelligence test based on information processing principles--the Leiden Diagnostic Test. The test was administered to two independent groups of children--one tested recently, another tested 25 years ago. Analyses of the test scores showed that over time, children's IQ scores increased at least 15 points for those in the higher SES group and 8 points for those in the middle SES group. In a two-factor solution, scores on the Spatial-Analytic factor increased more than scores on the Verbal factor. Inspection of the three-factor solution showed that gains on the Spatial-Analytic factor were about 0.9 SD, on the Memory factor 0.8 SD, and on the Verbal factor 0.6 SD. The finding that performance or fluid abilities, measuring on-the-spot problem-solving, are more susceptible to change over time than crystallized abilities, measuring the results of learning in the past, is consistent with our hypothesis. However, the finding that aspects of children's memory are also susceptible to change over time was unexpected. It is hypothesized that the working memory system may have become more efficient over time because more information has to be absorbed at a much younger age, and coping with a stimulating environment may require a more efficient memory system.