The percentage of children participating in school is a key societal outcome because children need to attend if they are to benefit from school. Two age groups are targeted in this outcome: 3- and 4-year-olds and 15- to 19-year-olds. Research suggests that early childhood education is associated with better performance later in school. Tracking students 15 to 19 years of age is another way of assessing a system’s success in serving students through completion of high school. High school graduation rates provide the final indicator of successful completion. The Organisation for Economic Co-operation and Development (OECD) tracks data across 30 member nations. In 2014, 42% of 3-year-olds and 68% of 4-year-olds in the United States participated in early childhood education. This level of participation ranked 27th and 28th respectively among OECD nations. In 2010 (there was no U.S. data in 2014), the participation rate for 15- to 19-year-olds was 81.7%, ranking the United States 24th among OECD nations. In 2014, the high school graduation rate was 82%, for a ranking of 21st among OECD nations. Comparative rankings are one way of benchmarking participation. In all cases, the United States lags behind 20 or more nations, suggesting very poor performance.