Barbara Kable packed up all her laboratory materials--her test tubes and flasks--more than a year ago when she was told that she would be moving to a renovated classroom at Chopticon High School for the start of the 1998-99 school year.

Then, Kable said this week, she and her colleagues in the school's science department "taught out of boxes" for half the school year, waiting six more months before they could actually move. Teachers and students could not perform laboratory experiments while they waited for their new classrooms, which were completed in the spring, said Kable, who has been at Chopticon High for 28 years.

But as they and their students return for the opening of classes today in St. Mary's County public schools, the science teachers say they are eager to start the new school year knowing that they will have permanent classrooms. Some of them were uprooted more than once last year.

"The last year and a half has been crazy," said Paul Sabota, a biology teacher.

Burgeoning populations have led to renovations and expansions of schools throughout Southern Maryland, forcing teachers and students to maneuver around construction areas on a daily basis. Many teachers have had to teach in trailer-like temporary classrooms. Others have had to move around to different classrooms as construction crews finished some areas and began work on others.

If all goes according to plan, this will be the last year that students and faculty will have to deal with the constant drilling and hammering that has been part of life at Chopticon High for two years.

"We're getting close," Principal John Ryan said.

When all is said and done, the $20 million project will result in an 800-seat auditorium, a larger cafeteria, a weight room, state-of-the-art theater and music rooms, and upgraded classrooms.

When Chopticon High resumes classes today, construction workers still will be roaming around the campus, tiling floors, rewiring some sections of the building, adding bleachers to the gymnasium and renovating several more classrooms.

Laurie Modrzejewski, who has taught English and Spanish at Chopticon for two years, has changed classrooms twice in the last year, and she expects to move once more in October.

Just two days before the start of the school year this week, Modrzejewski was preparing her classroom for the arrival of students and parents. As she unpacked boxes, she realized that she had lost some of her materials.

Outside her classroom, work crews were sweeping floors caked in sawdust. Around the corner, a sign warned people to stay away from a construction area. "It's hard to make this place look good when there are ceiling tiles missing," she said. "Once I get settled, it'll be a lot better."

In a nearby classroom, Karen Kowalski, an English teacher, opened boxes that will have to be packed again in a few months when the English wing of the school is finished. One corner of her temporary classroom serves as a storage area for history books. The room does not have a blackboard, so Kowalski said she will focus the first part of the school year on reading and writing.

"I can't really lecture because I can't write on a blackboard," she said.

Patty Kuzmick, on the other hand, was done moving. The music teacher's renovated space now includes a music library, practice rooms and doors wide enough to roll her grand piano through.

"I can't tell you the difference," Kuzmick said. "It was horrible. The ceiling was leaking for 15 years."

After 21 years, Kuzmick said, she finally feels as though she'll be teaching in a real classroom.

"We made something out of nothing."

CAPTION: Chemistry teacher Barbara Kable numbers new chemistry books in a long-awaited, newly renovated science classroom at Chopticon High.