Instrumentation, methodology, and analysis techniques were developed to measure changes in adolescent skills in the estimation of linear distance. Microcomputers were used to present and control the amount of information available to assist students in estimation. Three different levels of difficulty in estimating were developed and students estimated ten positions of a point on a vertical line within each level of difficulty. Strategies used by students to estimate were found, and a model was developed using regression analysis to allow for the separation of variance of trend and individual skill differences. This model was used to predict decreases in number of estimates and decreases in average time per estimate. The number of estimates per position decreased rapidly and a limit was soon achieved. Thus average time per estimate was used as a measure of skill. Students improved performance within the first two levels, but not within the most difficult level. Across levels, average performance improved in spite of increasing difficulty, and a transfer effect appeared to occur over time. It was concluded that micro-computers were a valuable instrument for gathering and recording data. The model using regression analysis was an effective tool to study estimation. Students used effective strategies and improved their estimation skill quickly. Learning did occur, but the level of difficulty of information or practice effect available while solving an estimation problem may limit the extent of improvement.