The 2012 results for USA, http://www.oecd.org/pisa/keyfindings/pisa-2012-results.htm, for Maths, Reading and Science show the gender gap to be better than the average with a trend towards constancy; ie contrary to the GP's claim. However, I wouldn't want to say on my cursory view of their summaries that the GP was wrong.
This is about to be slightly off topic, but:
You don't need to apologize for questioning. You should be encouraged to question. I've noticed this trend lately (some here, often on askscience/historians) where people preemptively apologize for asking for sources.
Just because you question their sources does not mean you are personally attacking them.
The 2012 results for USA, http://www.oecd.org/pisa/keyfindings/pisa-2012-results.htm, for Maths, Reading and Science show the gender gap to be better than the average with a trend towards constancy; ie contrary to the GP's claim. However, I wouldn't want to say on my cursory view of their summaries that the GP was wrong.