D.C. public school students performed slightly better on rigorous math and reading tests this spring than last but did not repeat the sizable improvement in test scores they achieved last school year, according to preliminary data released last night.

The fraction of students scoring "below basic"--the lowest level on the Stanford 9 Achievement Test--declined 1 percentage point in reading, to 27 percent, and 1.31 points in math, to 48 percent, according to a sampling of students who have taken the exam each of the last three school years.

From 1997 to 1998, the number of students scoring below basic in reading declined 6 percentage points, and the number scoring below basic in math dropped by nearly 8 points. Students who score below basic show little or no mastery of the skills needed for their grade level, Stanford 9 officials say.

D.C. School Superintendent Arlene Ackerman, who has made improving test scores a cornerstone of teacher and principal evaluations, student promotions and her entire reform effort, said she was "pleased" with the small gains.

"We don't want to downplay the fact that we made progress," Ackerman said last night at a meeting of the school system's Emergency Transitional Education Board of Trustees. "We should be proud. . . . We're not sliding back."

The school system has focused intensely on improving test scores, starting with a mammoth remedial program for 25,000 students last summer and continuing with tutorials after school and on Saturdays for low-performing students.

Officials last night cited a host of potential reasons that gains were not higher, including an exodus last fall of 3,600 students to public charter schools, whose scores are not included with those of the other public schools; a high number of students enrolling in the school system late in the academic year; and a failure to introduce reform programs at 23 low-performing schools because of delays in signing contracts to provide the services.

The complaints about the slowness of the city's procurement system, which Ackerman has cited as a major problem throughout the school year, sparked concern from the trustees.

"Children are suffering because we adults are not getting our acts together," said trustee M. Charito Kruvant. "We do a tremendous disservice to our children by not providing them what they deserved and what we promised."

Ackerman cautioned that the figures released last night were extremely preliminary, and she promised the trustees a more complete report at their meeting in early August. Among other things, the report will show whether students who score below basic have improved their raw scores and moved closer to "basic," the next achievement level; whether students who attended the summer and after-school tutorials improved; and whether those students who fled to charter schools were among the better-performing students last school year.

"I'm an achiever, so of course I'd want to see us make a 10-point gain," Ackerman said in an interview. "But am I happy that we made a modest gain? Yes."

The District began using the Stanford 9 test in 1997. Ackerman called results from that spring--which showed a large majority of the high school students tested scoring below basic in math and many scoring below basic in reading--"educational genocide."

School officials announced last year's gains earlier in June and in far more detail, including the percentages scoring at each of the four achievement levels--below basic, basic, proficient and advanced--broken down grade by grade. School-by-school analyses came months later.

Ackerman said similar data are not yet available this year because Stanford 9 officials are trying to answer more complicated questions: looking at the change in each student's scores from the previous year, analyzing which students left the system and studying whether remedial programs had an impact. In addition, computer coding errors and other glitches slowed the information sorting process at about 10 schools, she said.

That's why, even though individual test scores are being mailed home to parents of most public school students this week, systemwide results won't be known at least until August.

Officials did say last night that 90 percent of the city's 146 schools showed either a decline in the number of students scoring poorly or an increase in the number scoring well.