The aim of the current research is to measure the effectiveness of a program based on enjoyable learning in teaching mathematics to develop mathematical reasoning and some habits of mind among prep school students. The research used the experimental method; Where the main research sample consisted of a sample of (63) students of second year middle school, divided into: an experimental group (n =31) and a control group (n = 32). To achieve the research objectives research materials and search tools were prepared: the teacher’s guide, the Student’s Worksheets, Mathematical Reasoning Test, and Habits of Mind Test; The two research tools were applied before and after on the control and experimental groups. After the experimental treatment and testing the validity of the hypotheses, the results showed that the students of the experimental group outperformed the students of the control group in the test of mathematical reasoning as a whole (and for each of the test skills separately), and also the students of the experimental group outperformed the students of the control group in the test of habits of mind as a whole (and for each of the test skills separately); Therefore, the research recommended the necessity of preparing training courses and workshops for mathematics teachers to train them on how to teach using fun learning. Key words: Mathematical reasoning - Habits of mind - enjoyable learning.