This paper aims to predict the influence of personal factors of students on mathematical performance in primary education. This is an ex-post-facto study using the database from the TIMSS 2019 study in USA. The sample comprises 8601 American students of 4th grade (50.45% boys; 49.54% girls). An Exploratory Factor Analysis (EFA) and a Confirmatory Factor Analysis (CFA) were carried out on the 24 items from the student questionnaire on the mathematics teaching and learning process (KMO= .952). Four factors were identified: student´s attitude, anxiety, self-efficacy and teacher´s attitude. A multiple regression analysis was used to predict the influence of students’ factors on mathematical performance. Results show that self-efficacy is the factor that most contributes to performance and in which more gender differences are found, followed by math anxiety, in favor of boys, which explains the gender gap in the United States. Teacher´s attitude, which is the second factor that most contributes to performance, reinforces both student´s attitude and their self-efficacy. Number of books in the home has a great effect on students´ performance. Findings suggest the need to propose the teaching of mathematics from a more practical approach and provide more resources to schools in disadvantaged contexts.