According to a recent report, children’s reading performances have improved in the past decade. While 70% of fourth graders had weak reading skills in 2003, that rate dropped to 66% in 2013.

However, there are still significant differences in literacy rates among students across the country. In Massachusetts, just 53% of fourth graders were not proficient readers, the best among all states. In both Mississippi and New Mexico, on the other hand, 79% of kids in fourth grade were not proficient readers, worst in the nation.

Click here to see the states where children are struggling to read

A variety of factors contribute to a child’s chances of reaching reading proficiency. According to the Annie E. Casey Foundation’s report, “Brain research tells us that the first eight years are critical for building the foundation for future learning and emotional development.”

While literacy rates have improved nationwide, the gap in the ability of children from high- and low-income families has continued to widen. According to the Annie E. Casey Foundation’s report, “In every state children from low-income families are less likely to be reading than their higher-income peers, and in nearly all states, the gap increased over the past decade.”

Last year, 80% of fourth graders from low-income families were not proficient readers. Nationwide, less than half of kids the same age from higher-income families were not strong readers. In six of the 10 states where children struggled most to read, 85% of fourth graders from low-income families failed to meet proficiency levels.

Poverty rates were also higher in these states. The three states with the lowest proficiency rates for fourth graders — Mississippi, New Mexico, and Louisiana — also had the three highest poverty rates in the nation.

While the relationship is not clear, education expenditure could play a role in proficiency rates. A number of states where children struggled the most to read were also among the bottom 10 states in per-pupil expenditure in fiscal 2011. That year, per pupil spending exceeded $10,000 in only three of the 10 states with the lowest fourth grade reading proficiency scores. Nationwide, schools spent an average of $10,560 per pupil. Mississippi and Arizona spent less than $8,000 per student.

However, expenditure does not explain low performance. Alaska’s per student spending was the second-highest in the nation in 2011, but its fourth grade proficiency rates were among the worst last year.

To identify the states where children are struggling the most to read, 24/7 Wall St. reviewed data from “Early Reading Proficiency in the United States,” a 2014 report from the Annie E. Casey Foundation, a charitable organization focused on improving the lives of disadvantaged children. The foundation used figures from the National Assessment of Educational Progress for 2003 and 2013, and split classified students as coming from higher or lower-income families based on eligibility for the National School Lunch Program. We also reviewed data from the U.S. Census Bureau’s 2012 American Community Survey including poverty, income, immigration, and language-spoken statistics as well as educational attainment figures. Per pupil spending figures, also from the bureau, were considered for fiscal 2011. Gallup-Healthways Well-Being Index provided data on health outcomes and basic access to necessities.

These are the states where children are struggling the most to read.