Both Amazing Grace by Jonathan Kozol and The Jungle by Upton Sinclair describe the brutalizing and dehumanizing effects of poverty on decent people placed in intolerable circumstances. Both were written as pleas for social justice by authors who did massive amounts of research on the social conditions and everyday lives of the poor in major American cities.
The main differences have to do with the dates of publication and the way society changed in the interim. The Jungle was first published in 1906 and addressed conditions in Chicago; Amazing Grace appeared in 1995, almost a full century later, and discussed New York City's South Bronx neighborhood.
The first major difference has to do with race or ethnicity. The Jungle describes the plight of eastern European immigrants to Chicago. One of their main barriers to assimilation was language. As they were Caucasian, they had the opportunity to assimilate to middle class society if they could learn English and break out of the initial cycle of poverty. Although many European immigrants did suffer discrimination when they arrived in the United States, the lack of racial barriers makes such happy endings as that of Jurgis possible. In Amazing Grace, the communities being described are primarily black and Hispanic, bearing a legacy of slavery, on the one hand, and illegal immigration, on the other hand. Both of these communities are what Canadians term "visible minorities," meaning that they can suffer discrimination based on appearance, creating a far greater obstacle to social mobility.
Another major difference in the social conditions has to do with the prevalence of illegal drugs and drug dealers in the 1995 book, and the prevalence of guns. The fights described in Sinclair's work occur with fists, not guns, and thus people survived them. If Jurgis had attacked Connor with a gun, or guns had been present at other conflicts in the novel, the result would have been murders, not bruises, and the happy ending impossible.
Finally, there have been significant changes in medical knowledge and technology. In 1905 Chicago, the great danger was tuberculosis ("consumption"), and other infectious diseases that spread through overcrowded slums. In 1995, HIV had begun to spread through the South Bronx, especially by needle-sharing and prostitution. Part of Kozol's point, though, was that (unlike in 1905) the medical knowledge and wealth existed to solve these problems, but was being withheld in favor of giving tax cuts to the wealthy.