Yes, preschool makes a difference -- but what sort?

If you haven't already, you will be hearing much about something called the Perry Preschool Program. The program started in 1962, with the clearly stated purpose to determine whether preschool experience does (or does not) make a significant difference for youngsters through their 12 years of schooling.

Such studies are typically undertaken with two groups of children. The children in each group are as alike as possible (age, sex, family income, IQ, etc.). One group of these children is labeled "experimental;" the other is known as the "control" group.

Both sets of youngsters are given the same tests, asked the same questions, and in all possible ways measured both for physical ability and mental alertness. Then the experimental group is given something that the control group is not given; in the case of this study, that difference was formal preschool activities at the age of 4.

There were 28 four-year-olds chosen in 1962, only 13 of whom were in the experimental group. The next year's group was smaller, only 17. A third group (26) was picked in 1964, a fourth group (27) in 1965, and a final group of 25 in 1966. All told there were 123 black children with low IQs (ranging from 70 to 85) in poor families.

Every effort was made to match family circumstances, such as one parent, size of the family, income, living circumstances, and so forth.Over the ensuing years , nearly all of the children and their families continued to participate and agree to the constant testing and individual interviews.

In fact, with the exception of one major flaw, the research design is almost without fault, providing the results with strong integrity.

But the major flaw is serious. And while it does not call into question either the preliminary and now the long- term results -- that preschooling has an enormously positive effect -- it does raise a whole other set of issues.

The flaw: The same people who did the testing and research are the ones who designed and ran the preschool the experimental group attended. The Perry Preschool's goal: "to help children acquire the intellectual strengths they would need in school."

With such a goal, with specially trained teachers, and with the impetus to prove that the preschool experience would be more beneficial than a lack of same , it is hardly any wonder that the differences in both attitudes about schooling and actual measured achievements were greater for the experimental group than for the control group.

And in a way, the dice were loaded. The children in the control group, because they came from poor families and had either a single (working) parent or two working parents, received little of the intellectual stimulation and play activity which a child in an economically stable and intellectually active home might have.

It's not quite fair to say it's like offering piano lessons to 58 youngsters and no piano lessons to 65 youngsters and then giving piano tests to see which group does better! But it's close.

But then, the main point of the study was to show that a high portion of these children would have had trouble in school, gotten into trouble out of school, and become an economic burden on society if they had not had a good, strong, supportive, positive preschool experience.

And that's precisely what did happen. The kind and degree of preschooling the experimental group children received so improved them and prepared them so well for school that they outdone the control group in nearly every measure taken. And the measurements are still being taken, so that we will know more about entrance to higher education, jobs, and conditions of employment.

But it would be foolish to label preschool experience as the decisive factor -- that is, just any preschool. The Perry Preschool, administered by the High/Scope Foundation of Ypsilanti, Mich., was exceptional, taking advantage of the best developments in preschooling activity and superbly equipped (both personnel and materials).

much is made, for example, of the sort of encouragement the preschool teachers gave their little socioeconomically poor three- and four-year-olds. They instilled in these little ones the idea that they could succeed, and built preschool experiences around successes.

The preschool teachers encouraged the youngsters to think for themselves, sometimes to use paper and pencil, other times to experiment, and always to be inventive and curious.

Perhaps some way can be found, studying the material collected in the Perry Preschool Program, to determine just what sorts of preschool activities and teaching are essential if at 15 a youngster is going to be willing to struggle with an academically demanding class in Latin or chemistry or solid geometry or world history.

Of course preschooling is good -- and good for rich and poor alike. But some preschooling is not nearly as productive as some other.And what needs to be done now is to build from this point.To find out what makes a successful preschool.