The Lab School of Washington, a nonprofit organization devoted to helping children with learning disabilities, has bought the former Florence Crittenton Home in Northwest Washington.

The 3.6-acre property at 4759 Reservoir Rd. NW, in one of Washington's wealthiest neighborhoods, includes three buildings on a hill facing the Georgetown Reservoir.

The property had been for sale since June 1982 after the Florence Crittenton Home, a home for unwed mothers, closed because of financial difficulties and lack of residents.

The Lab School of Washington bought it last May for $2.4 million. The D.C. Board of Zoning Adjustment approved the Lab School's use of the buildings July 27.

"We were able to buy it because we have raised $450,000 in cash this year through donations," said Sally Smith, founder and executive director of the Lab School. She said the rest of the money was obtained through bank loans.

Smith, 54, said the school, originally at 1809 Phelps Place NW, wanted to move to a larger site so it could increase its enrollment of learning-disabled children, whose symptoms often include lack of concentration, poor speech, reading problems, clumsiness, immaturity and a short attention span.

"Our school doesn't accept mentally retarded children, who have a limited potential," Smith stressed. "Children who are learning disabled are those intelligent children who have unlimited potential.

"They aren't slow learners. Some of these children turned out to have a superior intelligence. The difficulty is that it is so subtle that the symptoms can only be discovered through learning."

The school, scheduled to open Wednesday, will have an enrollment of 122, Smith said.

She said the school tries to help learning disabled children get back to mainstream schools as soon as possible and to keep them current with children in traditional classrooms in such subjects as history, geography and science.

Achieving these goals requires individualized diagnostic teaching of reading, writing, spelling, arithmetic and perceptual skills, she said. Students work individually or in small groups and use a variety of visual aids, including talking books, tapes and films.

Tuition at the school is $7,800 to $8,000, Smith said. The city is paying the tuition for 50 District students and tuition for six Virginia students is funded by the state.

Tuition for the other students is paid by their parents or private groups.

"The tuition is high because of the individualization of each child's program," said Smith, who is in charge of the Learning Disabilities Program at American University.

"Everything is in such small groups that we need a teacher-student ratio of 3 to 10."

The projected annual budget of the school is about $1 million, she added.

The school now has a total part-time staff of 31 teachers, she said. Many are specialists in woodworking, graphic arts, music, dance and drama and receive intense training at the school before they begin teaching, she said.

Smith decided to open a school for children with learning disabilities in 1967 after she learned her 7-year-old son could not see the difference between a straight line and a curved line, although she was confident he could learn.

That year, Smith founded a school at the Kingsbury Diagnostic Center, a testing center for children with reading problems.

For the last 15 years, the school has helped up to 800 students with learning disabilities, Smith said.

Most of these children finished high school and attended college, including Harvard and Emory universities.

"The results are far greater than what we expected," Smith said. "As far as I know there is only one student who left our school and who failed to graduate from high school."

She said the school plans to do a follow-up study of each student who attended the school.

The Lab School became independent of the Kingsbury Center last year because, Smith said, "we want to be in charge of our own financial affairs, and we want to move to a large space where we can get more children and enlarge our services."

The purchase of the Florence Crittenton property has caused some concern among residents in the neighborhood that the school will mean an increase in traffic and noise in the community, according to Linda Maloof, executive director of Advisory Neighborhood Commission 3B.

There are already three schools in the area, she said.

But she added a majority of area residents support the Lab School and based on that support, the ANC 3B voted July 13 to back the purchase.

"We strongly support the Lab School," Maloof said. "To keep the impact to the minimum, we decided to restrict the school's projected enrollment over a four-year period from the original 310 to 250. We have also put in a resolution to ensure that they provide an adequate number of parking places."

Smith said the Lab School is trying to be a good neighbor.

"We are interested in conservation and will care for the land here. It is a beautiful area, and we want this area to be proud of us."