The research intended to compare the differences of mathematical communication skills between the students who are taught with RME and students who are taught with conventional learning approaches in terms of the school’s level and Mathematical Prior Knowledge (MPK). The research populations are all Islamic Senior High School (MA) students in Jakarta consist of 4 National Standard Schools (NSS) and 72 Regular Schools (RS). From two categories of schools level will be selected one of the school randomly. The research instruments used in this research are teaching materials on probability which is designed based on RME approach, MPK test, and mathematical communication skill test. The data will be analyzed by using the Mann-Whitney test and t-test. According to the data analysis, it was found that: (1) there are differences in mathematical communication skill between the students who are taught with RME approach and students who are taught with conventional learning approaches, as generally, or even both schools level and three categories of MPK, the RME learning approach given a better enhancement, (2) there are no significant interaction between learning approach and school level to the improvement of the students’ mathematical communication skills, (3) there are significant interaction between learning approaches and students’ MPK to the improvement of mathematical communication skills, RME approach contributed to better enhancement for low MPK students.

mathematical communication skills, RME approach, school’s level, Mathematical Prior Knowledge (MPK).