Student James Montalbano works with teacher Angela Benjamin on a Advanced Placement class in a file photo.

(AP Photo/Charles Dharapak)

Colorado schools rank 21st in the country in Education Week's annual Quality Counts report released Thursday.

The state scored an overall grade of C, the same grade as the nation. That ranking is the average of three separate indices: "Chance for Success," "K-12 Achievement," and "School Finance." Here's how Colorado performed in those categories.

Chance for Success: grade = B-, state rank = 12

This score factors in early foundations in learning, such as family income and parent education, math and reading skills during the school years, how many students go on to college, and annual income and employment.  

Colorado was sixth in the nation in the percent of eighth graders on target on national tests, and ninth in the nation for fourth graders reading proficiently on national tests. More adults here attend college compared to the national average – 48 percent compared to 40 percent.

But the state has one of the worst “poverty gaps” in the nation in terms of achievement. It ranks 45th in 8th-grade math, comparing scores of students who are eligible for free and reduced lunch to students who aren’t, and has the 41st-worst poverty gap for fourth graders in reading on national tests.

School Finance: grade = D+, state rank = 38

This category measures per-pupil spending levels and funding equity. Colorado spends about $2,700 less per student than the national average, accounting for regional cost differences.

K-12 Achievement Index (from 2014): grade = C, state rank = 11

Though this index wasn't updated this year, it's an important part of each state's overall score. It examines reading and math performance on National Assessment of Educational Progress tests, high school graduation rates, and AP exams scores.

Here's a table showing each state's grade:

Pre-K analysis

This year’s report also focuses on early-childhood education as its special theme.

Colorado earns a D and ranks 44th on the Early Education Index, which incorporates data from eight specific indicators. About half of three- and four-year-old kids are enrolled in preschool. That's about the same as the nationwide rate, but it 3 percent compared to 2008. The nation’s rate stayed flat.

In terms of the gap between poor children and non-poor children who attend pre-school, Colorado has a larger gap than the national average, ranking 47th in the nation. Enrollment rate for non-poor children minus poor children is 19.4 percent compared to national average of 15.8 percent.

Colorado scores poorly on the number of children who attend full-day pre-school, with less than a third of the state’s children doing so. That compares to half of children nationally.  And for kindergarten, about 60 percent of the state’s children attend full-day programs, compared to 75 percent nationally – making Colorado 47th in the nation.