In the aggregate, Idaho’s SAT scores were basically unchanged from 2016 — with high school juniors again scoring just shy of 1,000 on the test’s 1,600-point scale.

The scores also tended to underscore some basic demographic realities that color many test scores. Smaller and relatively affluent charter schools recorded the state’s highest SAT scores, while poorer rural schools and alternative schools had the state’s lowest test scores.

April’s SAT results provide a large sample size, since 89 percent of eligible Idaho high school juniors took the test. On “SAT Day,” juniors can take the test and satisfy a high school graduation requirement on the state’s nickel. SAT Day carries a taxpayer cost of about $1 million.

Here are some facts and figures from the April 2017 “SAT Day” — when 19,323 students took the college-entrance exam.

How did the big districts fare?

No strong pattern. Four of the state’s 10 largest districts improved; in Coeur d’Alene, the average score went up by 29 points.

The other six lost ground. In Twin Falls, the average score fell by 55 points.

Here’s the breakdown:

Who were the top performers?

Charter schools accounted for four of the five top average scores: North Idaho STEM Charter Academy, Rathdrum (average score, 1,290); Coeur d’Alene Charter Academy (1,278); Compass High School, Meridian (1,190); and North Star Charter High School, Eagle (1,170).

Rounding out the top five high schools: Renaissance High School, a school of choice operated by the West Ada School District (average score, 1,180).

The top-ranked school district: Moscow, with an average score of 1,098. The college-town school district is also relatively affluent, by Idaho standards; about 20 percent of Moscow High School students qualify for free or reduced-priced lunch, compared to the state average of 48 percent.

Who had the lowest scores?

Since the highest-performing schools were schools of choice with favorable demographics, it should come as no surprise that alternative high schools recorded the lowest average scores. The five lowest scores: Union High School, Nampa (796); Fruitland Preparatory Academy (794); Vallivue Academy, Caldwell (793); Mount Harrison Junior-Senior High School, Heyburn (777); and Tammany Alternative High School, Lewiston (733).

The district with the lowest average SAT score was Wilder — a district with one of the state’s highest poverty rates. Its average score came in at 839.

Who had the biggest improvements?

In the small Meadows Valley School District, the average score climbed from 861 to 965, a 104-point improvement.

The Patriot Center, an Emmett alternative school, recorded the largest improvement of any high school: a 143-point increase, from 770 in 2016 to 913 in 2017.

Who had the steepest decline?

Salmon River High School in Riggins. The average score fell from 1,123 in 2016 to 993 in 2017 — a 130-point drop that brought Salmon River’s scores more or less in line with the statewide average.

Idaho Education News data analyst Randy Schrader contributed to this report.

More reading: The 2017 SAT scores reveal a college-readiness gap. And facts and figures from the 2016 SAT Day.