In addition to the following questions about PIRLS, more FAQs about international assessments are available at: http://nces.ed.gov/surveys/international/faqs.asp.
The Progress in International Reading Literacy Study (PIRLS) is an international comparative study of the reading literacy of young students. The study focuses on the achievement and reading experiences of children in grades equivalent to 4th grade, and includes a written test of reading comprehension and a series of questionnaires focusing on factors associated with the development of reading literacy. Begun in 2001, PIRLS is conducted every 5 years. The third and most recent administration of PIRLS was in 2011, with 53 education systems (including countries and subnational entities) participating at grade 4.