Students who aren't yet reading at grade level by the end of 3rd grade can benefit from a year of retention, finds a recent study by Boston University's Wheelock Educational Policy Center. Third grade is a well-known benchmark year for literacy achievement; decades of research show that students who still struggle to read by 4th grade are more likely to have issues comprehending written material in future subjects, which has been linked to lower high school graduation rates and course performance. To improve early reading proficiency, around half of U.S. states now mandate or allow students who don't score high enough on a standardized literacy test to repeat 3rd grade.
Researchers studied Mississippi's efforts—under the Literacy-Based Promotion Act, passed in 2013—to understand how well its test-based promotions policy was working. They focused on a group of retained students who had scored within 20 points of passing proficiency in 3rd grade in 2014–15 and found that these students scored much higher on ELA standardized tests in 6th grade (scoring on average in the 62nd percentile) than did kids from that group who had narrowly moved on to 4th grade in the same year (scoring on average in the 20th percentile). Growth was especially pronounced among Black and Hispanic students who had been retained. (It's worth noting that retention didn't influence other outcomes in 6th grade, such as math scores or special education identification.)
Mississippi has gotten national attention for its reading score gains, the researchers say; average NAEP reading scores for 4th grade students in the state increased more than in any other state between 2013 and 2019. The state's apparent success is large enough, the researchers say, to suggest that extra time, alongside other supports, could be a useful factor in children's literacy development.