This research aimed at exploring the effectiveness of using Marzano's dimensions of learning model in teaching mathematics on achievement and geometric thinking of class nine basic educational. To achieve this, the researcher prepared a teaching guidebook in the unit of trigonometry, which is part of the school textbook, according to Marzano's dimensions of learning model. In addition, the researcher prepared two tests, an achievement test in the contents of the unit, and a geometric thinking test. Both tests were checked for validity and reliability. Sample of the research consisted of (56) female students from grade nine basic education schools in Muscat. This sample was divided into an experimental group, which studied the unit of trigonometry according to Marzano's model, and a control group, which studied the same unit by the normal class teaching method. The research results showed that: • There is a statistically significant difference at the level of significance (a < 0.05) between the mean score of the experimental group and the mean score of the control group in the post achievement test in favor of the experimental group. There is no statistically significant difference at the level of significance (a < 0.05) between the mean score of the experimental group and the mean score of the control group in the post geometric thinking test. The research ended with some recommendations such as encouraging teachers to apply Marzano's dimensions of learning model in their teaching, and try to use innovation teaching methods in order to teach mathematics with understanding and develop students' geometrical thinking skills