The aim of this study is to examine the effects of computer assisted instruction materials on approximate number skills of students with mathematics learning difficulties. The study was carried out with pretest-posttest quasi experimental method with a single subject. The participants of the study consist of a girl and two boys who attend 3rd grade at elementary school. The contents of the computer-aided instruction materials which have been designed consist of counting skills, place value concepts and addition subjects which are related to mathematics lesson's learning outcomes of 1st and 2nd grades of primary school. With the materials prepared, participants were given 75 lessons of individual instruction during five weeks, each weekdays and approximately 20-30 minutes a day. Dyscalculia screening tool and Panamath program were used as data collection tools. Panamath program calculates test response time, the percentage of accuracy and weber fraction data of participants. In the dot counting and comparison symbolic tests of DST, response time tests and number of correct answers of the participants were calculated, while mean absolute error were calculated in the mental number line tests. The findings of the study indicate that the approximate skills of the participants have developed and there has been significant increase in their speed of answering.