A recent readiness-for-kindergarten study revealed that almost half of all children who started kindergarten last year "were not ready." Obviously, "half" applies to some school districts and not to others.

But it's a finding that illustrates the importance of work being done by those developing more and better preschooling.

It could be equally important to consider maturation rates.

When children with precisely the same date of birth are compared, some are larger and some are smaller. Some have more ability to deal with ideas that lend themselves to academic measurement, and some have less. And some children do not have English as their home language -- or at least not the English used by those who devise the tests through which "achievement" is measured.

Commentaries in newspapers sometimes express surprise because "gaps" in test score averages -- between children of white and minority parents, and between children of higher- and lower-income parents -- do not seem to change (with a few very localized exceptions), in spite of widespread efforts to address the problem.

The gaps could be reduced substantially, I am convinced, if we would evaluate children in kindergarten to determine which ones need "a second year of kindergarten." Not a repetition of kindergarten but rather "a transition year," as it is called in California -- a year between kindergarten and first grade, with individualized catch-up opportunities before the child is put back on the school-grades escalator.

Two separate factors combine to exacerbate the problem: One, as noted, is the natural range of maturation differences among children born on the same day, month and year.

The other is that public school authorities use 12-month ranges of birth dates within which kindergarteners can be enrolled in a given class.

It's worth remembering that 12 months, to a 5-year-old, is 20 percent of a short life. That's a lot of life in which to mature just by getting older, in addition to the natural variations noted earlier. This matters a great deal when children are being measured in competition with classmates (which of course is how "gaps" are defined).

It takes certain expertise to measure differences in children's readiness to deal with academic learning. But it would be easy to identify those pupils who are the youngest entering kindergarten. When dealing with those who fail the reading and math tests at the end of third grade, are we finding out whether those who were youngest, within the 12-month range, when entering kindergarten also turned up, by a significantly larger proportion, among those who later failed? (Surely someone is doing this?)

In the 2011 session of the Minnesota Legislature, the House of Representatives passed a bill that would have mandated that all students who fail the end-of-third-grade standardized tests would have to repeat the third grade. But why torture little kids for three whole years -- until they have acquired such habits of failure that they cannot recover? Why not remedy many problems before it is too late, by providing a "transition year" early on for those who need it most? (There is evidence that those who fail the third-grade tests almost never achieve satisfactorily in future years. I assume they are being tracked as to their becoming future dropouts?)

What other remedies are thought to reduce gaps? One very prominent proposal is to level the playing field -- by providing that all preschool-aged children enroll in good preschool programs. This would help considerably because at present, on average, children who need preschooling least are getting the most, while those who need it most are getting the least.

But keep in mind that leveling the playing field -- providing equal-for-all amounts of preschooling -- would not mean also "leveling the players." The variations described earlier would remain -- the 12-month range in ages of those entering kindergarten, plus the naturally varying capacities for academic learning. The latter is of course influenced greatly by living in a wide variety of home cultures, including differences in the spoken home language, access to books and much else.

If we don't want failure to persist, let's not start with failure.

Howard Bergstrom, retired in Minneapolis, was formerly administrator of curriculum and instruction with school districts of Wayzata, Minn., and University City, Mo.