MARY Lou Hartley's third-grade science class was used to the five-foot-long corn snake draped somewhere other than in its cage. Its serpentine coils lent a certain ''Darwinian flavor'' to biology lessons. And besides, Mary Lou believed in running an open classroom - for everyone.
But things got a little too open when a student pointed to the snake (or at least the last two feet of it) uncoiled and slithering down a radiator pipe to the floor below. The pipe led to the principal's office. The sight of the tail descending the pipe led Miss Hartley to the principal's office as well. ''I had to use the stairs,'' Miss Hartley laughs as she reminisces over one of the funnier escapades in her 32-year teaching career.
''When I got to the office, the principal was standing at his door. There was a parent in the office with him. Calmly, he handed me a brown paper bag. It had a big bulge in it.'' To this day she is sure that parent left with a whole new idea about what an open classroom meant.
Miss Hartley will retire from teaching in June. So will thousands of teachers like her. Some states like California and New Jersey will see more than 40 percent of their teaching staffs leave the classroom in the next five years as many of the teachers who entered the profession after World War II reach retirement age.
With them will leave memories - about the way our country, our educational system, and our youth have evolved over the last 35 years. And these memories, woven into the very fabric of the schools these teachers have served, detail a record of unparalleled change.
For Miss Hartley, becoming a teacher was just the natural thing to do. ''There were not many careers open to women then, you know,'' the pert, white-haired trooper of countless classrooms says. Teaching would also give her more time with her own children.
''I think I started teaching at $2,000 a year,'' she says. ''In fact, when I signed the contract it was under $2,000 and by the time I started teaching it was a tiny bit above that, and I thought that was wonderful. You know, I had two kids and I was a single parent. Can you even picture living on that amount of money? Of course, I did live on that amount of money. I had to work in the summer, selling World Books.''
Today, young women have many other career choices. The teaching profession no longer has a monopoly on the services of women like Miss Hartley.
Would she go into teaching again if she had it to do over? ''I'd teach again without a second thought,'' she says, pointing to a corner of her classroom where a number of students are working. It's clear she can't wait to be over there with them. ''I'm just as curious as they are,'' she says.
Mary Jane Reed will also retire in June. She has been an elementary school educator for 35 years and, like Miss Hartley, has taught three generations of Minneapolis public school students. For her, answering the question of whether she would teach again is not so easy.
''I don't know. I would have to think it over, I just don't know. The other day I was speaking in front of a group and this woman came up to me and said, 'You should teach at the university.' You know why? She really meant it, because I was articulate. What she really thinks is that it doesn't take as much skill to teach kindergarten.''
''I thought, 'My dear woman, it is so simple to talk to you adults compared to living all day with two different groups of five-year-olds with the emotional commitment, the energy and strength, I need to relate to those little children.' Adults would value me more if I taught at the university. Well, that's hogwash. I'm still the same skillful, loving person no matter where I'm teaching,'' Miss Reed says.
Ever since both these women began teaching, there has been a need to adjust to new ideas. What's the biggest change they have seen in the way elementary schools are run?
''Mobility! The children stayed in the room all day. They only went out for gym and recess,'' says Miss Hartley. ''Now, there are times I feel like an air-traffic controller with all the special individualized programs children go to. We teach by the clock a lot more today,'' she says. ''And we have all the specialists. I'm not knocking specialists, because they do some great, great, wonderful things; but the kids are going in so many directions, to so many special classes outside mine today,'' says Miss Hartley.
The pressure of mobility is felt not only in the classroom, but in homes and families as well. ''We have children in kindergarten who have moved four times in one year,'' says Miss Reed. ''And I know in any class I have, up to half the children can come from a single-parent family.'' The movement of parents in and out of a young child's life is by far the most difficult challenge an elementary teacher faces, she says.
Due to the rising divorce rate, ''I had to get to know the parents in quite a different way today than I ever did, Miss Hartley says. ''I just had to get to know them. As teachers, we passed over the barrier about feeling uneasy with parent involvement in our classrooms.''
What about all the talk that children today are less disciplined? Both women pooh-pooh the idea. ''We have no more behavior problems today than we ever did. What we have is more hurting kids,'' says Miss Hartley.
And to meet this very real hurt, a teacher today needs a greater degree of emotional stability than ever before. ''I could survive emotionally with 40 students when I started,'' says Miss Reed. ''Today, 25 are more than enough, because so many come with such deep needs.''
One memory Miss Reed will always treasure is that of a five-year-old bringing her a long-stemmed red rose - two little fists reaching up, one clutching a tangle of bright red petals, the other the detached green stem.
In many ways the memory of the crumpled petals typifies the bitter-sweet ambivalence many teachers feel about their profession. For Miss Reed, leaving the classroom because of teacher burnout was not an option. It has been for many others.
For both teachers, television is like a monkey hanging around the necks of all their children. ''Its influence is just everywhere,'' and it has a negative impact by and large, not a positive one, they say.
''You can bemoan the change brought about by TV, or you can deal with it,'' says Miss Hartley. ''You must be more of a sociologist today than when I started ,'' which was in a very traditional classroom.
Now, she finds herself in an open school, where grade levels are not solely determined by age - and where students learn at a pace pretty much set by themselves. ''And I always have to have at least two sets of dolls in the room, because the children are so much more multiracial, multiethnic. This was never the case. It's a real difference, and I believe a real benefit of the public schools,'' says Miss Reed.
Do they have any advice for someone entering their profession today? Yes. Love kids. Know your subject matter. Stay abreast of early-childhood learning theory, as there is ''a lot of good research in that area.'' And in your heart of hearts, to paraphrase the last line of Robert Frost's poem ''Birches,'' know that ''One could do worse than be a teacher of children.''