You're definitely right about this one getting asked pretty frequently, but I'm not a smart enough wiki to be able to link to all the related articles, so I'll try to shift some for your teacher.

Population density and urbanization are probably two of the key factors in determining the manpower shortage of the South. The southern states did not urbanize at a similar rate to those of the North post Independence. While some southern historians have pointed to the economic importance of Charleston and New Orleans as evidence of the southern urban core, I have always found this argument weak when compared to the network of towns found in Massachusetts, Connecticut, New Jersey, and Pennsylvania at the same time. The two port cities acted as a clearing house for the agrarian products of the south, but did no encourage the same level of guild participation, working fraternal orders, and other significant late 18th century signs of the new 'middling' class of the First Industrial Revolution.

The southern plantation owners had vast tracts of land and slaves to work them, leaving poor whites to live on the periphery of southern society. Some free middling whites might take on roles in local government such as sheriff or later in the period mechanics and other late industrial tasks, but the plantation strove to be self sufficient with things such as bakeries, blacksmiths, and other facilities existing on the plantation itself. Essentially what we can say is that the agrarian ideal of the plantations led to a lack of free people not directly participating in the plantation economy and thereby not leading to increased urbanization and population growth.

The north did not have this system for the most part and farms were smaller as a result. The new west states such as Michigan and Ohio were settled by small holders which meant land ended up distributed in more hands which again would lead to population growth as the farms became viable. Immigrants entering the United States would come in search of cheap available land and jobs and would find both of these mostly in the North.

The South generally had the most experienced and highly trained officers because it was a tradition for the elite of the south to attend military academies and participate in the American armed forces. Interestingly it was not as common in the American Navy which fielded a much higher number of competent Northern officers. Lee was considered an exceptionally brilliant commander as was 'Stonewall' Jackson. Their counterparts in the form of a Burnside, Hooker, or McClellan were far less capable. I am also a firm believer that the North approached the war with kid gloves in the outset and that actions such as the burning of the Shenandoah and Sherman's scorched earth policy(too late I know) would have helped sap the Southern states ability to feed itself and forced it to capitulate earlier. The truth is that Historians and I believe a policy of this group is not to speculate on the coulda, woulda, shoulda, of history.

The South lost the civil war for several reasons:

1. Tactically. In the end the South lost because of the effectiveness of the Anaconda plan to choke it's ability to move its products abroad and pay for the war. It eventually lost on the battlefield due to attrition and in some places incompetence especially in the Western theatre. Grant's siege of Richmond was successful and Lee's assault on Pennsylvania was not. Many actions can be pointed to as "heroic" as commanders attempted to slow down Union advances in Georgia and Tennessee, but were ineffective at stopping them.
2. Economics - The southern system was outdated and could not produce an economic base from which to supply an army with the necessary industrial equipment of the newly developing shape of warfare. Southern plantations weren't so economically viable as to afford rifled cannons, ironclad 'monitors', repeating rifles, torpedos(mines)...bla bla in the same capacity as an industrialized and urbanized polity like the North. They tried, and their examples are held up as ingenuity, gritty determination, and overcoming the odds. No one really ever says that about Springfield Mass. producing literally 100's of thousands of high quality weapons until the finally days of the war. 3)Politically - Outside powers, especially England did not recognize the South. The concept of an agrarian state sitting alongside the USA may have seemed like a good idea at one point in the relationship, but India was in direct competition with Alabama for the cotton mills in the UK at the same time. The concept of slave ownership was dipping below the horizon in most European political discourse. It was the death rattle for this system that a century prior had been quite widespread.

Good Pop-History that influenced this 'White Trash' - by Nancy Isenberg 'Confederates in the Attic' - by Tony Horwitz

Sadly the rest of my library is in storage.