Research reports major concerns over classification and measurement for students with limited English proficiency (LEP). A poor operational definition of the English language proficiency construct and validity concerns about existing language proficiency tests are among these issues. Decisions on including LEP students in large-scale assessments such as the National Assessment of Educational Progress (NAEP) may be directly influenced by some of these factors. Poor relationships between the existing LEP classification codes with English proficiency and achievement test scores raise concern over the validity of the LEP classification system. These factors have contributed to inconsistencies in LEP classification across districts and states. Criteria used for the inclusion of LEP students in NAEP need to be more objectively defined. Based on the recommendations of existing research, the appropriate levels of English language proficiency for participation in NAEP should be determined by reliable and valid English language proficiency measures. With funding through a competitive bidding process authorized under the No Child Left Behind section on "Enhanced Assessment Instruments," there are national efforts currently underway in developing English proficiency tests that can be used to provide valid measures of students' level of English proficiency. These efforts should be guided by the relevant theory and research findings, otherwise past problems relating to the validity of English proficiency tests may recur. Multiple criteria including valid and reliable measures of students' level of English proficiency could help with a more consistent decision-making process for the inclusion of LEP students.