A study was conducted to determine if the inclusion of a foreign language requirement in high schools may have a positive effect on students performance on standardized English exams From a sample of 100 high schools 50 of which had a foreign language requirement and 50 of which did not it was found that the average score on the English proficiency exam was 25 higher for the students having a foreign language requirement What confounding variables may be present that would invalidate the conclusion that requiring a foreign language in high school increases English language proficiency