Tom Collier, principal of Paul Junior High, has read about the "crisis in American education," the "rising tide of mediocrity" that threatens the nation's public schools.

So why is this man smiling?

To some degree, his is an I-told-you- so smile. He recalled a column I had written about his school, back in 1978, pointing out that 9th graders at Paul were, on average, scoring lower in math and reading than were the 6th graders at some of the elementary schools that feed into Paul. It was one reason, I wrote, why so many parents, though committed to the public schools, were sending their junior-high children to private schools.

Collier made two points at the time: first, that the reported averages concealed some truly outstanding achievement and, second, that "lack of ability was not the sole reason for students' low test scores."

Vindication is sweet. The latest test results were published last week, and Paul's 9th graders scored an average of 9.7 in reading (seventh month of the ninth grade, or just one month below the national norm), and 10.1 in math. The comparable scores at the time of the 1978 column were 7.5 in reading and 6.3 in math.

Some component scores were still more encouraging: 10.4 in reading vocabulary, 10.5 in language mechanics, 11.1 in math concepts. "We are talking about gains of three and four full school years since the time of that column," Collier says, not even trying to suppress his grin.

Academic gains at Paul outstrip citywide gains, which, in themselves, constitute some of the best news Washingtonians have had in years. For the first time since the D.C. schools began district-wide testing five years ago, elementary school youngsters are scoring at national norms. Junior and senior high gains were still greater, but not enough to catch up to national norms. At no level did average test scores decline.

What accounts for the good news? Interestingly enough, the superintendent, members of the school board and principals are not agreed. Superintendent Floretta McKenzie credits volunteer tutors and the use of teacher aides to reduce class sizes; school board president David Eaton cites smoother relations between the board and the superintendent; board member Barbara Lett Simmons attributes it to mid-year promotions for qualified students.

Collier credits two things: the Competency Based Curriculum, which sets clear instructional goals for every subject, and something called the Intensified Junior High School Instructional Program, a citywide program that he modified to his own specifications.

To an outsider, the changes seem to stem from one central factor: the decision to get serious about educating the city's youngsters. The children themselves appear to be accepting the new seriousness.

At Paul, every student now has four reading periods a week, geared to specific subject areas but designed to improve reading skills. Wednesdays are devoted to special math instruction.

Even the test-taking atmosphere has been changed. Collier now separates the boys from the girls, "to reduce peer annoyance," and furnishes staff help in administering the tests. ("Some home room teachers can't control their own rooms.")

"We don't threaten the students," he said. "We motivate them to do as well as they can. I'm convinced that one of the reasons for our low scores in the past is that the students didn't take the testing seriously--an attitude that may have been unconsciously transmitted by teachers."

The changes at Paul show up not just in the test scores but in the cleaner rest rooms, the graffiti-less walls, the litter-free corridors and the absence of evidence of drug and alcohol use.

What the changes suggest is that talking about education is not the same thing as getting serious about education, and that the children know the difference.