Someone with mathematical connection skills can have a deep understanding of mathematics and have a complete view of mathematics without being separated. From the observations, it was found that the mathematical connections of the grade 11 science students in one of the Christian high schools in Rantepao were still low, where all students could not solve the problem with the mathematical connection indicator beyond the minimum score that already given by the school. This study aims to determine whether or not the CORE model can improve students' mathematical connections. The data sources used are student test sheets, mentor checklist sheets, student reflection journals, and researcher reflection journals. The research method used by researchers is classroom action research according to Pelton. The results showed an increase in students' mathematical connections with the application of the Connecting, Organizing, Reflecting, Extending models of XI IPA students at one of the Christian High Schools in Rantepao.