This research aimed to examine the effectiveness of the INSTAD strategy in comparison to other teaching strategies such as Inquiry, student team's achievement division (STAD), and lecture method, to reduce the gap of higher order thinking skills between Upper Academic (UA) and Lower Academic (LA) groups of students. The research participants were 136 7th grade students in total, which consisted of two groups of 36 UA and 36 LA students. The students were selected through a stratified random sampling from 27 Public Junior High Schools in Surakarta, Indonesia. The treatment classes were determined through an intact group. The research design employed pre-test-post-test non-equivalent control group of quasi experiment. The higher order thinking skills were measured by essay test sheet as an instrument. Data were analysed by utilizing ANCOVA with the pre-test score as the covariate. The findings revealed that INSTAD have optimally improved higher order thinking skills in comparison with the Inquiry, STAD, and lecture method. INSTAD's were proven able to reduce the gap of higher order thinking skills between UA and LA students rather than Inquiry, STAD, and lecture method as teaching strategies.