Considering that primary school and middle school students could learn more rapidly and permanently with tangible experiences, it is significant to utilize material that materialize the topic in instruction. The objective of the present study is to analyze the effect of the number strip material developed by the author on mathematical achievements and attitudes of the students. The study utilized a mixed methodology that combined qualitative and quantitative research methods. The study sample

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... cluded 86 (43 study group and 43 control) 4th grade students who were attending a primary school in the Bağlar district in Diyarbakır province during the 2016-2017 academic year. The achievement test and attitude scale developed by the author were used to collect the study data. The achievement test and attitude scale were applied as both pretest and posttest to the control and study groups. The data obtained were analyzed with SPSS 24.0 software and it was determined that the achievement test reliability coefficient (Kuder-Richardson 20) was 0.819 and attitude scale reliability coefficient (Cronbach Alpha) was 0.946. The qualitative data were obtained with the interview conducted with the classroom teacher after the application, and content analysis was conducted on the data. Study findings demonstrated that the developed number strip material concretized and simplified the topic, attracted the interest and curiosity of the students, resulted in active participation of the students in the class, rendered the course pleasant and entertaining, influenced the attitudes of the students positively towards mathematics and improved the achievements of the students.