Encouraging the idea of a growth mindset in which students believe that they can improve their ability, as opposed to a fixed mindset, has been suggested as an effective and relatively cheap approach to improving student attainment at school. This paper offers a comprehensive review of the evidence from growth mindset interventions. After a rigorous search, screening and evaluation, the inclusion criteria led to 24 studies. All were randomised control trials (RCTs) focused on growth mindset of intelligence interventions for school-age children and included output measures for academic performance assessment. Their findings reveal that the strongest studies, characterised by larger sample sizes, minimal missing data and high data quality, exhibit null or very small effect sizes, ranging from Cohen's d = -0.01 to +0.065. Additionally, certain findings raise concerns about a potential conflict-of-interest bias, suggesting that some negative or null results may remain unpublished. The review identifies four evaluations with a high degree of trustworthiness and non-conflict of interest. Among these, two studies indicate no discernible impact, while the other two show a very small impact. Given these findings, we found evidence that suggest that growth mindset interventions targeted for school-age students, do not have much or any relevant impact in academic achievement. It is therefore not advisable for schools, school districts or governments to allocate significant time or resources to the implementation of growth mindset interventions for school-age students, as the anticipated outcomes are likely to be either null or very modest. However, if there is an opportunity to implement such interventions at a minimal or negligible cost, or as part of another objective, it might be reasonable to proceed with them, considering the potential for a small positive impact.