4. Discussion
The findings from this study were consistent with findings internationally that the explicit teaching of thinking skills was beneficial for students from all schools participating in the intervention (Adey et al., 2002; Zohar & Peled, 2008). Specifically in response to the research question, however, the magnitude of the effect of the Thinking Science cognitive acceleration programme on the academically selective school students’ levels of cognition compared with students who did not participate in the Thinking Science cognitive acceleration programme was indicated by a large effect size (d = 0.995). Using Cohen (1988)conventions as a guide, d of 0.20 can be considered small, a d of 0.50 is medium, and a d of 0.80 is large. Hattie (2009), recently suggested that an effect size of 1.0 is equivalent to “advancing children’s learning by 2–3 years”. The results from