In this research we investigated female elementary students’ level of mastery over science and mathematics content and explained the nature of relationship between students’ level of mastery and learnability of content in elementary level science and mathematics. This research is mixed-method in nature. The quantitative analyses are based on correlation method, Structural Equation Modeling and comparing means. 914 female students of public senior elementary schools in Kashan were recruited. Minimum sample size determined by GPower software for each grade and students were selected by cluster random sampling method. The needed data for fourth and fifth graders were gathered through researcher-made cumulative tests; the data related to sixth graders were gathered through cumulative formal and standard exams taken from the students of this grade in the end of semester. Content validity of tests was verified by connoisseur teachers in each grade and was confirmed by structural equation modelling. The reliability of researcher-made tests was estimated around 0/77 to 0/86 according to Cronbach's Alpha coefficient. For explaining the quantitative findings, we implemented 9 interviews with experienced and expert teachers which were selected through purposeful sampling method. The interview questions were according to our findings in the quantitative part of the research. The main analysis revealed that students learning is significantly lower than the mastery level in almost half of the science syllabus and all of the mathematics syllabus. Teachers pointed out several factor in student’s inability in mastering math and science content that learnability of the content of these subjects, as one of the most fundamental and influential factors, however, seems to require more attention.