Anecdotally I've heard many Mexicans (who have gone to American schools) claim that Mexican schools are better than US schools, and apparently so have other people. PISA lets us test this assertion empirically. Furthermore, the PISA scores for the science section are available broken down by ethnicity in the US, which allows us to make a more in depth comparison.
On the combined science literacy scale in the United States, Black (non-Hispanic) students (409) and Hispanic students (439) scored lower, on average, than White (non-Hispanic) students (523), Asian (non-Hispanic) students (499), and students of more than one race (non-Hispanic) (501).
The DF (Mexico City) with a score of 445.11 and Queretaro with a score of 440.43 are the only states that do better (barely) than US Hispanics (439). Since the difference between Hispanic students in the US and Mexican students is so great, we can probably lay the blame on the school system and teachers in Mexico.
The average score for all groups in the US was 489 and the average score for Mexico was 409, the test has a standard deviation of a 100 points so that would put Mexico .8 deviations below the US, which means that the average Mexican student scores at the 21st percentile in the US.
The results are averages and of course do not mean that there aren't individuals of extraordinary abilities, just that the percentage who meet a high threshold is much lower in Mexico. And in fact the percentage of students that reach the highest two levels in the exam is 3% in Mexico, compared to an average of 9% across all OECD countries
Not everything is bad news, now that teachers can no longer inherit or sell their jobs, and are chosen by a nationwide exam, test scores will probably go up.
Update: Only girls were tested in Chihuahua, and only high school students took the test in Michoacan