The Extended Foreign Language (EFL) program is a "school within a school" dual language program in which students are instructed in both English and a language other than English (Spanish or French) with one hour of daily instruction in that language. Most of the schools participating in the program implement the English/Spanish version of dual language instruction. The implementation of the EFL program began in Miami-Dade County Public Schools (M-DCPS) in 1997. In 2012-2013, the District initiated an expansion of the EFL program that began with grade K students and expanded by one grade level per academic year. In 2016-2017, many elementary schools had implemented the EFL program in their entire grade K-5 span. Generally, students are placed into the EFL program in Grade K at the request of their parents and depending on the number of seats available. The goal of this Research Brief is to compare the achievement of students in the EFL program with that of their peers and to determine whether learning the second language distracts students from mastering core academic subjects. Because the selection and placement of students into the program are not random, one needs to employ a suitable analytic methodology to enable proper comparisons.