AIN'T NO MAKIN' IT Leveled Aspirations in a Low-Income Neighborhood By Jay MacLeod Westview Press. 198 pages $26.95; paperback, $12.95

IN SOCIETIES where people's status is ordained by law, the question of how to account for class differences has an obvious answer. But in industrial democracies like our own, where in theory people can become whatever they want, there is a lot of room for argument about why the rich are rich and the poor are poor. In general, the right says that in America, status is a product of individual effort, and the left says that we have an unacknowledged class system that assigns people their places.

Depending on your inclinations, you can see the American poor as people who had the same chance as everyone else, and blew it, or as people who never had any chance at all. Sociological studies show that children are likely to be of the same class as their parents, and this would appear to support the left's vision of a country with a strong hereditary class system.

On the other hand, sociological field work among the poor usually shows that poor children don't act like Horatio Alger heroes, either -- they don't study hard, the boys commit petty crimes, the girls have babies out of wedlock, and so on. This, it would seem, is fodder for the right. But here the left splits, bitterly, into two camps. Radicals say that when poor children, at just the time when they should be grabbing at opportunity, behave self-destructively, what they're actually doing is demonstrating that they have figured out that the idea of opportunity for them is a total sham, and constructing an alternative value system that will help them to survive in the brutal little world to which America has assigned them.

What might be called the right wing of the left disagrees, and says the self-destructive behavior is the product less of the economic system than of the customs of a subculture bred by poverty, which could be changed without fundamental alteration of our society.

Into this ideological swamp strides Jay MacLeod, with a study -- adapted from his senior thesis at an unnamed university that's pretty obviously Harvard -- of teen-age boys in a housing project. MacLeod's sympathies are completely with the radicals. He repeatedly indicates that he regards as ridiculous the idea that there is real opportunity in America; if a few poor people make it, it only lends legitimacy to the system that oppresses the rest. Capitalism is "a race by the many for relatively few positions of wealth and prestige," in which "the great majority are automatically bound to be disappointed." Black advancement since the '60s is only "alleged," meaning, presumably, that our society wouldn't have allowed it truly to take place.

If the poor seem to lack the middle-class virtues, it's either because they're not really virtues ("the conventional nuclear family is not the natural . . . form of household organization") or because the system is blind to the equally valid, but different, virtues that the poor do have ("the educational system's curricula, pedagogy, and evaluative criteria favor the interests of the upper classes").

MacLeod's main subjects are the members of a gang called the Hallway Hangers, a group so sublimely bad (to use their favorite self-description) that, to cite just one example, one member once "repeatedly stabbed himself in the head in a fit of masochistic machismo." The Hangers' code -- hanging out, drinking, taking drugs, stealing, fighting, skipping school -- is repeatedly explained by MacLeod as the product of a normal, rational, even "perceptive" and "insightful," evaluation of the hand that capitalist society has dealt them.

That MacLeod had the patience and the courage to get inside the Hangers' world as completely as he did is impressive, and his lengthy quotes from them are gripping. Still, if this were a book solely about the Hangers, it would be a pretty standard piece of left-wing sociology, distinguished neither by unusually graceful writing nor by an original point.

WHAT MAKES it different is its secondary characters, the members of another gang in the same housing project called the Brothers. The Hangers are predominately white (and viciously racist); the Brothers are mostly black. Where the Hangers are bad, the Brothers are good: they are ambitious, they study hard, they listen to their parents, they have steady girlfriends, and they stay away from drinking and drugs. In other words, they don't behave according to the script. The odds against them are, in MacLeod's view, even longer than the odds against the Hangers, because the Brothers are blacks in a racist society, and yet they persist in harboring "excessive ambitions" that show that, unlike the analytically sophisticated Hangers, they "are unaware of the processes that work to hinder their performance."

It took intellectual courage for MacLeod to introduce evidence that doesn't fit well with his overall theory, and to say, heretically, that the Brothers show that culture as well as economics can influence behavior. His explanation of why the Brothers act differently from the Hangers is convincing, too: as blacks and as relative newcomers to the housing project, they believe that more opportunity is open to them than was to their parents, whereas the Hangers, whose families have lived for several generations in the project and haven't recently been freed from legal restraints on their success, see their poverty as inescapable.

A sociologist with different inclinations might use the contrast to make a case for mainstream liberalism, and say that strong family life, a determination to stay in school, and a helping hand from the government really can make a difference in the lives of poor people. But this is almost exactly the opposite of what MacLeod believes, so he is left with the problem of how to fit the Brothers into the context of his book.

His solution is to portray them as chumps for believing that there will be any payoff from their adherence to middle-class values. They don't do as well in school as you'd expect from their dedication to it, and when they graduate, MacLeod is convinced, they won't be able to find good jobs. While the Hangers will fail and blame society for it, the Brothers will fail and blame themselves, and the pain of this future self-hatred makes it "an open question whether the Hallway Hangers or the Brothers are worse off."

In the Hangers, MacLeod detects an ideology that values sticking with the group over individual achievement; in the grand tradition of intellectuals predicting the emergence of a radical American proletariat, he sees this as "a seed that could flower into an affirmation of class solidarity." He ends the book with a flurry of vague Marxist phrasemaking about the need for "fundamental change," "class conflict," and "a genuinely open society," followed by a final note of pity for the Brothers for their not finding more fault with the economic system.

The trouble is that the Brothers, by MacLeod's own evidence, are already, even before their entrance into the economic race, clearly less miserable than the Hallway Hangers. The Hangers are addicts to drugs and alcohol, are likely to end up in prison, and are incapable of having real relationships with women. The Brothers have it rough, but they don't have any of these problems. In the future, MacLeod himself admits, in a passage that runs against the grain of the rest of the book, that "most of the Brothers will end up members of the stable working class, generally employed in jobs that are toward the bottom of the occupational ladder but that afford some security."

t may be an open question to MacLeod which group is worse off, but it isn't to me. There is a slight feeling of attitudinizing about MacLeod's hostility to an ethic of individual achievement ("My first recommendation is that the achievement ideology must go"), especially since, as much as he sees the folly of other people's adherence to it, he appears to have fallen under its sway himself. The book jacket photograph of MacLeod shows him in the garb of a young urban tough -- close-cropped hair, t-shirt, earring, a strand of barbed wire visible in the background -- but underneath the picture it says, "Jay MacLeod is a Rhodes Scholar . . ." Evidently hanging around with the Hangers has affected his dress more than his life-course. You shouldn't judge a book by its jacket, but purely on scholarly grounds, MacLeod's iron insistence that ambition among the poor is useless, even counterproductive, is nowhere near confirmed by his research, and so it looks more like a posture than an insight.

Nicholas Lemann is national correspondent of The Atlantic.