By simple requiring that children master one grade before being promoted to the next, school officials here have moved their system from near the bottom of national rankings to considerably above average in many subjects.

Starting with the 1973-74 school year, Greensville County School Supt. Sam A. Owen ended the commonly accepted practice of social promotions - passing a student regardless of academic performance. As a result, 1,100 of the county's 3,700 students were forced to repeat a grade in 1975.

"People say it's psychologically bad to retain in a grade," says Supt. Owen. "It's psychologically a whole lot wores to hand a child a diploma and have him find out later that he doesn't know anything."

"We had students who were going through school knowing very little about reading and writing," said Owen. "They were getting what I was beginning to call a 'rubber diploma.' I was getting sick and tired of reading in the papers every year about how badly we were doing."

Getting students to perform at grade level required an overhaul of the grading procedure and massive retentions of students in the same grade for two years, but the results have been impressive.

Discipline problems have abated, the dropout rate has fallen, and scores onstandardized tests have gone up. In the seventh grade, for example, average scores on nationwide reading tests rose from the 28th to 64th percentile; general language ability scores from the 37th to the 73d percentile and mathematics from the 26th to the 62d percentile. Virtually all other grade levels and performance in all other subjects also registered gains.

(Reporting test scores in percentiles ranks students in comparison to other students in the same grade across the nation. A score at the 50th percentile means the student has done better than half the students tested and worse than half)

When he first announced the promotions policy, Owen said, blacks - who account for 65 per cent of the students in the system - called him a bigot. Whites called him a Communist. In the first year of the plan, he backed down on a proposal to require 1,300 students to repeat a year.

"The parents complained that their children had received passing grades all year, some of them As and Bs," Owen recalled. "In those cases, we decided to let the parents have their choice and about 500 of them wanted their children promoted."

No such option was offered the follwoing year, and 1,100 students were held back. Last year, 695 students were required to repeat a grade. School officials say they expect the number of retentions to decline each year and they note that more than half of those held back now are repeating a half year, not a full year.

To accommodate such students, officials have set up a series of "in between" grades. Fifth-grade students who have learned something but not enough to do sixth-grade work, for example, are placed in a grade called "56".

With the rising test scores, community opposition to the promotion policy has warned. Owen now has posted a huge sign outside his office: "Greensville County School Board Office - where Promotion in Based on Achievement."

His efforts have drawn both the national press and education journals to Greeensville County, on the North Carolina border about 100 miles inland. CBS news arrived in Emporia to talk to Owen and film scenes in the schools. School superintendents from as far as Piqua, Ohio, and Pinellas County, Florida, have come to talk with Owen and visit the schools. There have been inquiries from state education officials in California and Georgia. This weekend, Owen flew to Vero Beach, Fla., to brief a group of interested citizens there.

"What Owen has done is something lots of people have talked about," says George Weber, associate director of the Washington-based Council for Basic Education. "But he has really gone ahead and done it. It's courageous, forward looking and constructive."

The merchanics of Owen's plan are to subject each student in the school system to a battery of standardized tests twice a year, once in the fall and once in the spring. Scores on those tests, plus teacher evaluations, form the basis of a decision on whether to promote. If a teacher wants to promote a student who has scored below his or her grade level on a test, the teacher must explain why in writing. Additionally, teachers have been instructed to give students an honest evaluation of their progress on report cards and to emphasize basics in the classrooms.

"If I go to the hospital to have a doctor take my temperature, I hope it's going to be 98.6. But I want the doctor to tell me what it really is, not what I hope it is," says Owen.

In the four years the plan has been in effect, the classroom atmosphere has changed substantially, teachers say.

"The students seem to care more about what they're doing because they know they've got to learn it to get promoted," said Jane Lee, a reading teacher at Belfield Elementary School.

"Before, students knew they would be promoted if they just came to school a certain number of days and sat in a classroom."

Secondary schools supervisor Deborah Ranick recalled teaching a 9th grade social studies class when the policy of social promotions was in effect.

"I found a majority of the students could not read the textbook. We had tremendous discipline problems. Many of them have been cleared up now," she said.