With SAT reading scores at a ­four-decade low and results for some Washington area schools down sharply, we asked around after last week’s College Board report to find out what happened.

We learned that the college entrance test, once a rite of passage for elite students, is increasingly being built into the high school experience for everyone, and that a new generation of college prospects will need far more academic preparation for a successful transition. Here are some key factors behind the scores.

First, a technical shift

The College Board has traditionally calculated average SAT scores for graduating seniors through March of that year. For the Class of 2011, it began including scores from tests taken through June.

The switch added about 50,000 test- takers, or 3 percent of the total. While not a huge number, these late entrants to the college process are more likely to be “VERY low performers,” a College Board spokeswoman said in an e-mail.

Some school systems recalculated last year’s average to account for the late test-takers. In Montgomery County, the new students brought the 2010 average score down to 1647 from 1653 on a 2400-point scale.

More test-takers than ever

A record 1.65 million graduating seniors took the test, more than half of the Class of 2011. That increase was reflected in nearly every Washington area school system. In Arlington County, the portion of seniors who took the test increased to 73 percent from 69 percent. In Loudoun County, participation rose to 80 percent from 73 percent, and in Calvert County, it grew to 65 percent from 60 percent.

Greater participation often brings lower scores.

Another factor is the growing popularity of the ACT, a rival college entrance exam. While the SAT is dominant in the Washington area, more local seniors are trying both tests, rather than seeking to improve their SAT scores by retaking it.

Exams not just for college-goers

Increasingly, the SAT and the ACT are being used to encourage students to apply to college, not just to enable them.

Delaware has a new four-year contract with the College Board to administer the SAT to all high school juniors. Texas offers all students vouchers to take the SAT or ACT for free, and Idaho is moving in the same direction. Seven states offer the ACT to all juniors: Colorado, Illinois, Kentucky, Michigan, North Dakota, Tennessee and Wyoming.

“Obviously, not all these students go to college, but it helps to focus them on the idea of going to college,” said Ed Colby, an ACT spokesman.

Trends to watch

Grade inflation? Even as scores declined over the past decade, the portion of students reporting that they earned an A average in school has grown to 45 percent from 41 percent, according to a College Board survey of SAT test-takers.

Gender gap? Even though fewer boys go to college than girls, boys are outscoring girls on the SAT. In 2011, boys scored 531 on the math section, 31 points above girls, and they scored 500 on reading, five points above girls. On the writing section, girls were ahead by 14 points with an average score of 496.