Within the framework of the revised taxonomy of educational objectives created by Anderson and Krathwohl, this study attempted to describe the design and examine the learning outcomes of an intervention focused on the development of higher order thinking at an elementary education setting. A class of 21 sixth graders participated in the project, which had a duration of 10 months and followed a mixed methods research design. For the needs of the intervention 23 lessons and assignment tasks were designed and implemented. The analysis of the data collected illustrated that overall, students' performance on higher order thinking tasks has improved. Furthermore, students with high academic achievements at school scored higher on thinking assignments, followed by average achievers. Low achieving students obtained the lowest scores, but in comparison to their classmates had on average the greatest progress of all. The findings of the study are discussed in the light of relevant literature to reveal that the process of developing higher order thinking is a demanding and multidimensional endeavour which requires extensive and profound changes in the practice of teaching.