Preschoolers' strategic behavior was examined on a task in which they must decide whether two arrays are the same. Fifty-six 3- and 4-year-olds selected doors to open which exposed parts of the arrays. Children made moderate use of an appropriate "vertical-pairs" strategy - viewing spatially corresponding parts of the two arrays - and it facilitated performance. Telling nonstrategic children to use the strategy or executing it for them improved their same-different judgments. However, increased spontaneous production of the vertical-pairs strategy over trials did not consistently improve judgments, which suggests a strategy utilization deficiency. Other microgenetic analyses revealed that children tended to use several strategies over the trials and that strategy changes often were not developmentally progressive or driven by failure of another strategy. The discussion addressed production and utilization deficiencies and the diversity of strategy development.