In the morning on the last full day of school, it was easy to be deceived. There were a fall-like coolness in the air, and a fall-like studiousness in the classroom at Spring Hill Elementary in McLean.

Stubby-legged first graders at stubby-legged desks were hard at work on one last project, one last serious effort before the celebration began. Soon there would be games, a picnic and ice cream sundaes to mark their big step into second grade.

With crayons in hand they lettered, "When I grow up . . ." on construction paper, making a folder to hold their essays on the same subject.

"I would like to be a teacher because I like to be a teacher," wrote Carla Ford, "and then the men would say look at that pretty girl and then they would say look at them pretty legs."

There were others:

"I think I'll be an artist when I grow up because I've seen pictures artists have done and I like them. And if I can be an artist I would paint everything in sight. And if my mother saw it, she would get very mad!! And she would get very mad at me for painting everything! She would say, 'You can't be an artist anymore.' This would make me so mad that I would paint her,' "Shannon Werner had written.

"When I grow up I will be a nurse. When I grow up and when I have to give a shot if the patient screams I will say that is just tough!!!!" said Anne Rewey.

Even while the first graders worked, their mood began to change. "Are we going?" asked Brian Hobbs as they began to clear away the debris.

The day, after all, was to be different.

"You know, this is the very last full day of school," teacher Nikki Heinlein reminded them. "The next full day you'll be in second grade."

"I'd rather stay here," said Gary Shenk.

"I'd rather you did too, but you have to go on," said Heinlein. "Ms. Heinlein never gets out of first grade."

Shortly, Heinlein told them, they would go outside where there was an array of games to play. Then they would come back in for the hot dogs and hamburger patties brought from home, and take them outside to be cooked on a charcoal grill.

"Is it a Weber?" several young voices asked.

Then they would play some more, their teacher said, and, finally, they would come back in for ice cream sundaes which they would construct themselves.

On the way out, the first graders filed past another class project - a papier mache stegosaurus. There were pats and hugs and inspection for cracks and fissures in his papier mache hide.

With one ear next to the dinosaur's side and another hand tapping time against it, Lauren Garrison said, "Listen to his heart beat."

"What does he eat?" asked an adult. "You know . . . little juicy plants," said Bryan Brohm, giving a Latin name for the plants. They're extinct now."

On the playground there were soccer, T-ball (a baseball-like game), jump-ropes, bowling with plastic pins, a rubberized version of horseshoes, jungle gyms, hula hoops, badminton, bean bag toss into plastic milk cartons, relays, tug-of-war, jai alai, board and card games and an Irish setter that had strayed onto the playground. There were also younger brothers and sisters visiting with the mothers who had come to help with the cookout.

"I hate to see them go," said Heinlein, a teacher for 10 years, as she watched the youngsters on the playground. "Some of them move and write to you - You're really part of a growing family when you start teaching," she said.

Among her students there, were mixed feelings about the end of school and leaving first grade. There was none of the unrestrained glee about leaving school for the summer that characterizes some of the upper grades, none of the acquired distaste.

There was some anticipation of learning more in the second grade. What more is there to learn after first grade? "Times," said Dana Drews. "I think they teach you times."

Back in the classroom, Heinlein prepared her first graders (one of four first grade classes in a school of about 900 moderately affluent students) for a tour of the second grade rooms. "How many can name the second grade teachers? . . . You'll be in one of the rooms next year, and all of them are very nice, so you'll be lucky," she told them.

With Tracy Wilkinson as the leader of the line, the soon-to-be-second-graders filed into the terrain they would take over. "The desks are different from ours," said Mark King, running his fingers across a larger desk.

From room to room they went, with some students lingering behind. Johnny Webb stopped at the first room to look over a topographical model of different types of terrain. "Canyons," he said. "Oh, this is cool."

Back in their own room, Heinlein spread out paper plates full of peanuts and marsh-mallows, a can of chocolate syrup, a container of topping, and cartons of ice cream for the sundaes. "I know how we'll line up," she said. "Everybody whose first name starts with Z first."

"I'm a zebra," said Shenk.

Then she skipped around. "Everybody whose first name starts with A," she said.

"I'm an allosaurus," said Bryan Prohm.

"It's Bryan, Brian, Brian, Bobby and Bradley," said Bradley Cue, as the B's lined up.

"I'm mushing mine," said Craig Kolasch, as his classmates lined up for seconds. "We're going to stick to our chairs and can't go home," he said, as ice cream began to show up on faces, shirts, tables and chairs.

Then it was story time and a rowdy visit to the music room as last-day frenzy began to set in. Back in the room for one final bit of first grade, the students, following instructions, drew pictures of a cat, a flower, a sun and themselves and wrote short essays on leaving first grade.

"I feel good about going to second grade because I feel proud of myself," wrote Bobby Weinhold.

Vicky Carter, who would not be back the next day, report card day, got hers early and prepared to go "Vicky, what am I going to say to you?" said Heinlein, picking her up in a hug. "Bye, Vicky," said her classmates.

The others picked up jackets and lunch pails and lined up at the door leading from their first grade room. For the record, besides those already named and Maggie Jameson who was absent, they were Sean Housholder, Cam Lewis, Brian McCoy, Doug Smith, Nick Vroustouris, Kerry Benjamin, MuLan Chan-Randel, Caroline Chung, Jenifer Eaton, Pam Maze, Lara Semchyshyn, Sara Snell and Jody Ternisky.

Then the final bell rang.