This research which was participated in by 98 Grade 12 students enrolled for the school year 2022 – 2023 under the Humanities and Social Sciences Strand was an attempt to find whether the use of activating strategies, written and non–written, improved the level of critical thinking skills of the participants. Using a one–group pretest–posttest design, it gathered information on the use of written and non–written activating strategies using a survey questionnaire and on the level of critical thinking skills using a test. Both instruments were teacher–made and expert-validated. Results revealed that for the respondents, the use of written and non–written activating strategies is generally accepted. Their critical thinking skills can be described as ranging from needs improvement to satisfactory based for almost all skills before the use of activating strategies, but after its implementation, their scores have drastically shifted from very satisfactory up to outstanding. The test of correlation also revealed no significant relationship among the variables except for some variables. The use of activating strategies have also revealed that it improved the critical thinking skills of the respondents. Thus, its use must be encouraged especially when trying to present new lessons and if skills acquisition is desired.