When did Shop Class and Home Economics disappear from the American School curriculum?

Well, it hasn't. But the question might be asked "why" did shop class and home ec. largely disappear from school curricula?

Now, the answer to this is more interesting, and more debatable.

One could be that the American funding programme for schooling is intensely and intrinsically class biased, as it comes from local taxes. Other school systems fund public schools in other ways, state, provincial, federal, etc. This means that wealthy people get good schools, and poor folks get poor schools. But England has a similar system, so a comparable test would probably be fruitful here.

Another argument would to put the history of public schooling into context, historically and material, and expand from there. That's the track I'd probably take. So public schooling was originally relatively unpopular, many thought that it was basically a government plot to produced worker-drones.^1 Remember, people were not terribly happy with waged labour in the 1800's, they saw it akin to "wage-slavery," excepting the fact that capitalists had no need to take care of their employees, as they were formally "free" to negotiate wages. There's lots of good work on this, particularly on the "loom girls," who had their own newspapers and reading groups and such (for an interesting example of these sources see The Industrial Worker by Norman Ware). But, capitalists increasingly needed workers who were literate, so "the public school system." There was, of course, education before this, but it tended to be for the elite. This is basically the system we had before the labour peace of the post-war era, when masses of working class people actually got to go to university. But that's a different story (see Novak, That Noble Dream for more).

My argument would be that schools are a basically training grounds for the basic needs capitalists feel that feed the economy, and with the shifting of American capitalists' interests, so goes the school system.^2

So when America was a more lunch-bucket kind of country, and moderately more socially democratic (post-war to the early 1970's, before the massive investment in automation, offshoring, and deskilling, and the concomitantly reinvigorated war on labour) these skills were useful for capitalists; ie: business owners needed a proletariat who had a functioning understanding of basic mechanical tasks.^3 Externalising this training to the public sector meant that they basically had a semi-skilled workforce available upon graduation. Currently, a "good factory job" is basically extant in auto, and very little else.

For home economics, these were largely job training for the profession of "homekeeper." Socially useful employment, albeit unwaged. Capital needs to socially reproduce itself, and a nuclear family is a good way of externalising the costs of the actual (re)production of future proletarians. Capitalists externalise the cost of creating new workers to the workers themselves, and the training for that is also paid by the workers, through local taxes. So these skills were taught to (largely) young women, so they could be utilised in the home, for social reproduction. Now that women are largely in the workforce, these skills are no longer needed in the same way that they were before. At least from the perspective of capital.

So what happened to elements of job training? Well, computers are a much larger part of schooling, as they're needed in the wider economy. Also, the decline of the general Arts undergraduate degree has dovetailed on this (the "useless" degrees so denigrated by people who dislike knowing something that does not have immediate utility for the (re)production of capitalism). Furthermore, the specific training of mechanics and carpentry are now further externalised to the individual; if one wants to become a certified mechanic, head to trade school and pay for it yourself.

So the shifts in the needs of capital have produced shifts in the public school system.

Samuel Bowles and Herbert Gintis, Schooling in Capitalist America: Educational Reform and the Contradictions of Economic Life (New York: Basic Books, 1976).
Joel Spring, The American School, 1642-1985: Varieties of Historical Interpretation and the Foundations and Development of American Education (New York: Longman, 1986); Charles Sellers, The Market Revolution: Jacksonian America, 1815-1846 (New York: Oxford University Press, 1991).
Elizabeth Fones-Wolf, Selling Free Enterprise: The Business Assault on Labor and Liberalism, 1945-1960 (Urbana: University of Illinois Press, 1992).