**Abstract:**
Number sense is the general comprehension of numbers, operations, and the relationships which involve numbers. Based on previous prevalence studies, there are about 3–6 % of the population who have disabilities to understand the number sense. Thus, the computer technologies and mobile games play an essential role to develop the students with number sense, as it will be a tools to improve their mathematical and logical thinking. The main goal of this paper is to design a new educational math game named as 123GO to develop a basic mathematical skills of students with number sense. This study explores the measuring consideration for the usability of proposed educational math game (123GO) by using the usability testing which adopted to assess student’s motivation towards learning basic mathematical skills. During the usability testing session, the data observations of students are recorded. The usability testing data were quantified to measure the effectiveness, efficiency and satisfaction. The results showed that students' interest when using this game to teach them basic mathematical skills.

**Keywords:**
Number Sense, Mathematical Skills, Educational Games, Computer Technologies.