Final answer:
The statement that is not true about NAFTA is the claim of economic stagnation in Mexico; on the contrary, Mexico experienced expansion in trade and increased productivity in certain sectors post-NAFTA.
Step-by-step explanation:
Of the statements regarding the North American Free Trade Agreement (NAFTA), the one that is not true is that there has been economic stagnation in Mexico. After NAFTA's implementation, there was expansion in trade and foreign investment, and while it's true there has been a contraction in manufacturing employment in the United States and that Mexican wages remain low relative to U.S. manufacturing wages, Mexico has not experienced a decline in productivity rates. In fact, the agreement led to job creation in some sectors and bolstered the maquila industry.