Students starting school this fall may be the most tested ever.

There will be national tests and state tests and commercial tests to predict how well the youngsters will do on state tests. In 18 states, tests determine whether a high school senior will get a real diploma or something less, like a certificate of completion, come spring of 1999. Other states are planning such a requirement.No wonder then that states and private companies are training teachers to give tests, understand the results, report them and use them to improve instruction.

"Once you tell the kids that this is what this test is all about, it makes much more sense to them, too, and they come in with a whole different attitude," said Barbara Lee, who teaches seventh- and eighth-graders at Apalachicola High School in Florida.

Lee and some of her students spent six weeks this summer learning the ins and outs of Florida's reading and math standardized tests.

Her training was paid for by the state but given by Kaplan Educational Centers, the test-preparation company better known for helping college-bound students with the ACT and SAT.

Supporters say the tests encourage high standards and increase accountability. Critics argue that too much testing can dramatically shift the focus from teaching and learning as discovery to preparing students for tests, or "teaching to the test." In addition, worries linger that blacks and Hispanics, because of economic and language barriers, do less well.

Nevertheless, all states but Nebraska and Iowa require tests at different grades, usually starting with the third or fourth, according to the Council of Chief State School Officers. Iowa has a voluntary program that most districts take part in, and Nebraska plans to introduce statewide tests.

Test results often determine whether principals keep their jobs and teachers get raises and even whether some schools are allowed to stay open.

And in Texas, Gov. George W. Bush has proposed using state tests to determine whether children should move from one grade to the next. Waco schools have already done so, starting with first-graders.

Interest in measuring student performance has increased since 1983, when the "Nation at Risk" report found serious troubles with the quality of education. Performance on national measures indicates that millions of Americans have become high school seniors, even graduated, without learning to read or do math at a basic level. At the same time, national college admissions tests and other studies show evidence of grade inflation.

"The tests and reporting appear to be hurting kids' and teachers' morale and love of learning and making teachers' jobs more stressful," said Gail Jones, a University of North Carolina-Chapel Hill associate professor of education who conducted a mail survey of teachers in her state.

Some said they gave more tests, more worksheets and more lectures than they otherwise would.