This "The Final Nail In Growth Mindset's Coffin" article (http://www.learningspy.co.uk/psychology/nail-growth-mindsets-coffin/ …) and this "Growth Mindset Replicates!" article (http://marginalrevolution.com/marginalrevolution/2018/03/growth-mindset-replicates.html …) are summaries of the same study. Never trust any third-party interpretation of a result, including mine.
Both summaries agree: If you look at grade point average on a 4 point scale (A=4, B=3 etc), this intervention increases the GPA by 0.03 points; about 3% of the way from a B to an A. Statistically significant, but tiny. Probably real, but not important.