Reading requires an inventory to assess student’s level of thinking as a reader so that a teacher could plan remediation schemes to help the students achieve their optimum potential as readers by employing the strategies of remediation and provide enrichment schemes to sustain the ability of advanced readers and help those who are struggling in reading. One significant emerging issue recently is that students are greatly influenced by social media and online games, a common phenomenon that exists as the internet grows. This study seeks to determine the reading inventory which aims to develop the critical thinking reading of the students which is one of the very important skills in the 21st century, particularly among the elementary students of Mater Dei College. This embarks to address basic problems in coping with thinking skills which are lifetime skills. This study made use of the quasi-experimental design (Johnson, 2014) since data are gathered twice through the pretest and posttest. Primarily, it aimed to determine the entry and exit critical thinking reading levels of the students as shown in their pretest and post-test results and to find out further if there is a significant improvement after the given interventions. Results show that among the ninety (90) students involved during the pretest, seven (7), or 7.78% are at the independent level, seventy-five (75), or 88.33 % are at the instructional level, and eight (8), or 8.89% are in the frustration level. However, during the posttest, twenty (20) or 22.22% belong to the independent level, sixty-two (62) or 68.89% are in the instructional level, and eight (8), or 8.89% are in the frustration level. Overall, it suggests that there is an increase of 14.44% in the number of students at the instructional level.