The main purpose of this quantitative study was to investigate whether middle school students’ number sense skills and attitudes towards mathematics provide a useful measure to predict their mathematics achievement levels as they were assessed with schools entrance examinations. A sample was drawn from private foundation schools in Ankara. Data consisted of number sense test, attitude towards mathematics scale, TEOG mathematics scores, and mathematics school grades. The collected data were analyzed first with descriptive statistics. Then, a multiple regression approach was used to further analyze the data. Statistically significant and relatively moderate relationships were found between number sense skills, mathematics achievement and attitude towards mathematic. As a result of the multiple regression analysis, it can be concluded that number sense skills and attitude towards mathematics can be useful to predict to some extent mathematics achievement of students.