Aileen McQuillan, 22, walked into Room 110-C of Patrick Henry Elementary School in Arlington yesterday and began teaching reading comprehension to 15 summer school students as Oakridge Elementary School Principal Betty Belt sat in a corner of the room watching.

McQuillan, a Vienna resident and a May graduate of James Madison University, is a finalist in Arlington's search for 10 new elementary school teachers. Belt, a veteran of Arlington County schools, was in class to evaluate McQuillan's performance as part of an unusual new hiring procedure designed to weed out candidates who, simply put, can't teach.

The program, the first of its kind in the Washington area and one of the first in the nation, has already helped school administrators discover dramatic flaws in several finalists.

Lilla Wise, the school district's assistant personnel director, said that one finalist who tried out last week incorrectly taught a "basic math concept."

"We previously used the same process every district uses," Wise said. "Then we realized that there was one thing we didn't know about the candidates: how they teach."

The school district received 400 applications for 10 elementary school slots open this fall. Wise, who directs the screening process, said the initial group was narrowed down to the 26 finalists now trying out in the classroom. The new hiring procedure is limited to prospective elementary school teachers.

The evaluations began last week and will continue until tomorrow, when hiring decisions will be made. Principals from several of Arlington's 18 elementary schools are voluntarily evaluating the candidates, who teach 45-minute lessons.

McQuillan, who majored in early childhood education in college, didn't seem nervous during the reading lesson she had prepared for the summer school class, which featured Peter the Parrot, a puppet McQuillan uses to teach adjective usage. Belt jotted down notes and laughed with the students, who seemed to find McQuillan's lesson entertaining.

"This gives us a chance to see if the teacher fits in with the philosophy and flavor of the school," Belt said. "Also, an applicant can snooker you in an interview, but never in the classroom. This is going to give us a selective new group of teachers."

Education professionals interviewed generally approved of Arlington's new plan. Sam Sava, executive director of the National Association of Elementary School Principals, said that to his knowledge, "Arlington is setting a precedent."

"This will add to the knowledge a principal has about a teacher, and it certainly forces a person to demonstrate the skills he or she may have," Sava said. But he warned that "some teachers begin to show their pluses after they get into the classroom; true teaching takes place once a teacher knows the children's needs."

Dorothy Stambaugh, the chairwoman of the Arlington County School Board and a National School Boards Association administrator, endorsed the new program, calling it "the logical next step" in Arlington's hiring process. "This is yet another reading of these people. I'd like to see it go district-wide."

But a Fairfax County School District official said that the program would not work in his district.

"We had to hire 300 teachers to start the school year," said Warren Eisenhower, the assistant superintendent for personnel services who noted that several midwestern school districts observe prospective teachers in the classroom. "If you are only hiring a few teachers, you could be in a position to do that. We draw teachers from outside the area, and our size is constraining."

Wise said most Arlington candidates were recruited in Virginia. McQuillan was recruited from James Madison in Harrisonburg.

What are McQuillan's chances? School administrators won't say, but the 15 summer school students groaned when McQuillan said her lesson was over and she had to leave.

"Now, that tells you something," Wise said.