This study aimed to determine the mathematical reasoning skills of children in the area of Measurement and Data Analysis-Probability. First, Evaluation Instrument for the Early Mathematical Reasoning Skills is developed, its validity and reliability is performed. Furthermore, variables such as the effect of child gender, age, institution attended and part/full time attendance to the institution, total duration of preschool attendance as well as educational background of their parents were analyzed. The study group is composed of randomly selected 204 children of typical development in x at the age of 60-74 months attending dependent and independent kindergarten, private preschools, daycare centers and kindergartens of Ministry of National Education. Data were collected using Evaluation Instrument for the Early Mathematical Reasoning Skills that is type of holistic rubric and Child Information Form that was developed by the researcher. The instrument developed was found to be reliable and valid. No significant difference was found between the scores of reasoning areas and types of boys and girls.Keywords: preschool math, reasoning, measurement, data analysis, probability. Extended AbstractPurpose and Significance: Mathematics is one of the areas that help determine the reasoning skills of children clearly. By considering the educational materials used and math activities practiced, how children access to information and their ways of achieving this aim can be understood. Investigation of mathematical reasoning skills of children in the areas of Measurement and Data Analysis-Probability is significant for enhancing the number of related activities as well as their quality. Furthermore, it helps teachers who have reservations of conducting activities in these fields to see the related skills and their applicability to the preschool education such as activities of numbers, shapes, matching and comparing.Methods: Early Mathematical Reasoning Skills Evaluation Tool was developed along with its validity and reliability studies to identify the mathematical reasoning skills of children in the field of Measurement, Data Analysis and Probability. Moreover, variables affecting the mathematical reasoning skills of children in the fields of Measurement and Data Analysis-Probability were examined. The study group of this research was 204 children aged 60-74 months with typical developmental patterns that were selected randomly from 10 preschool.

Probabilistic reasoning needs careful consideration for the development of the child's ability to interrogate and predict the likelihood based on the findings from the evaluation of various situations or events. Children, hence, will begin to experience metacognitive skills such as considering different causes and effects, decision-making and interpreting. This study aims to explore the probabilistic reasoning skills of preschool children according to the influential variables of gender and age. Typically developing 123 children who are enrolled in the city-centre preschools in Ankara constitute the study group. In the study, five questions were asked in the probability section of the Evaluation Instrument for the Early Mathematical Reasoning Skills developed by Ergül (2014) were posed to identify the probabilistic reasoning skills of the children. Each child was treated individually to gather detailed findings. Children's explanations to the probability questions were evaluated in detail through the use of rubrics. Findings reveal that girls and boys do not differ significantly in their probabilistic reasoning skills; but, in line with the recent literature, these skills improve as they grow up.Keywords: Preschool, probability, probabilistic reasoning, rubric, mathematics Makale Türü Özgün MakaleÖz: Olasılıksal akıl yürütme, çocukların farklı durum ya da olaydaki verileri değerlendirme, değerlendirme sonucu elde edilen veriye göre olabilirlik durumunu sorgulama ve tahminlerde bulunma becerilerinin gelişimi için dikkatle ele alınmalıdır. Bu sayede çocuklar farklı nedenleri ve sonuçları görme, karar verme ve yorumlama gibi üst zihinsel becerileri yaşama geçirmeye başlayacaktır. Bu çalışmanın amacı, okul öncesi dönem çocuklarının olasılıksal akıl yürütme becerilerinin incelenmesidir. Bu becerilere etki edebileceği düşünülen cinsiyet ve yaş değişkenleri de incelenmiştir. Araştırmanın çalışma grubunu, Ankara şehir merkezindeki okul öncesi eğitim kurumlarına devam eden ve normal gelişim gösteren 123 çocuk oluşturmaktadır. Çalışmada çocukların olasılıksal akıl yürütme becerilerini belirlemek için, Ergül (2014) tarafından geliştirilen Erken Matematiksel Akıl Yürütme Becerileri Değerlendirme Aracı'nın olasılık bölümünden beş soru sorulmuştur. Ayrıntılı veriler elde edebilmek için her çocukla bireysel olarak uygulama yapılmıştır. Çocukların olasılık sorularına getirdikleri açıklamalar, rubrikler aracılığıyla ayrıntılı olarak değerlendirilmiştir. Bulgulara göre kız ve erkek çocukların olasılıksal akıl yürütme becerilerinde anlamlı bir fark bulunmazken, son yıllardaki alan yazına paralel olarak bu becerilerin yaşla birlikte gelişme gösterdiği ortaya çıkmıştır.