Short answer: The formal introduction occurred in 1893 when Report of the Committee of Ten on Secondary School Studies, With the Reports of the Conferences Arranged by the Committee from the National Education Association (NEA) was published.^1
[A note about the long answer: the creation of the modern curriculum was overwhelmingly done by white men, focused generally on the future interests of white boys. Although most teachers were women and more girls completed high school than boys, they were not a part of these conversations; nor were people of color. The best resource for learning about curriculum decisions in Black high schools is the book FIRST CLASS by Alison Stewart.]
Long answer: US history has been a part of classrooms as long there's been American classrooms. A Philadelphia printer created one of the country's first textbooks called Introduction to the History of America: Designed to Instruct American Youth in the Elements of the History of Their Own Country in 1787. He took (i.e. plagiarized) large chunks of books written for adults and repurposed them as a book for schoolchildren.^2 An 1828 report on the NY School for the Deaf reported students were "well-versed" in history and listed textbooks such as Parley's History of the United States and The First Book of History (New England and New York).^3 In A Visit to Boston Schools, the author reported listening during history recitation when the teacher called out to the students, "English kings!" They replied, in unison, with the names from "Egbert to Victoria."^4 These kinds of recitations were common and reflect to the presence of history in the typical grammar school (typically ages 6 through 13 or 14) classroom curriculum. ^5
To your question, though, "history class" itself wasn't really established until the idea of discrete units of course study gained widescale acceptance classes following the Committee of Ten's report and the creation of the Carnegie Unit^6.
The Committee's work was spearheaded by Charles Eliot, Harvard's president from 1869 to 1909. At a Massachusetts teachers' conference in 1884, teachers wrote a resolution drawing attention to the lack of communication between high school and college faculties.^7 Eliot was among those who acknowledged the resolution and over the next few years, colleges and schools in New England began to talk to each other about expectations, curriculum, and what it meant to be an educated citizen.
These conversations, pushed forward by Eliot, often included the message that the young people who showed up for college were woefully unprepared. The cause of this preparation gap was attributed to, in part, the presence of different approaches to curriculum in secondary schools. Some schools followed a Classical Program (Greek, Latin, mathematics) while others taught a Modern or English Program (French, literature, geography, physics, political sciences, etc.). Although students did have some choice about which type of school to enroll in, choice was limited by distance, cost, and in some cases, what college the student planned on attending. The NEA, the largest organization for educators in the country, was interested in the issue as it posed problems for its members. One example was the delay the eventual president of Columbia experienced when he applied to the university. His public school hadn't prepared him to take Columbia's Greek/Latin entrance exam so he had to wait a year and study under a private tutor before applying.
During the period of time that school leaders, known as "school men", (because, well, they were men. Who ran schools) were communicating with college professors, American historians were establishing professional organizations such as the American Historical Association (AHA) and advocating for history education in schools. In 1892, when the NEA decided they wanted to solve the problem of disparate curriculum in high schools, American historians were ready to represent.
Even figuring out how to solve the problem, though, took a great deal of negotiation. The NEA had to determine who would sit on the committee and what content areas should be discussed. This required nation-wide data collection, report writing, and advocacy. ^7 Amusingly, one of the challenges the NEA report writers ran into was around nomenclature - some "colleges" were universities that required entrance exams, some "academies" were more like college for students younger than 19, and no one was really sure what constituted a pure "classical" education.
A consensus emerged that, to be successful, the system needed uniformity. The "scientific management" craze was just on the horizon and the idea of standardization was viewed as a way to improve all children's access to quality education. Ten white men - one the principal of a girl's school, one the president of a woman's college - representing different educational organizations convened to answer a series of questions related to content. All the men on the Committee were considered moderates - none were advocates for pure Classical or pure Modern curriculum - and all were open to the idea of uniformity in varying degrees. The Committee met on November 9, 1892 and created nine categories to be explored by a work group. The "History, Civil Government, and Political Economy" workgroup met in Madison, Wisconsin on December 28-30, 1892. The history workgroup included principals, college presidents, and members of the AHA. Each work group provided recommendations. The history group's started:
They even went so far as to break down the eight years of study, with American history in year 4 and 7 as well as embedded in other courses. Like most of the workgroups, they realized they had little control over colleges' entrance criteria and elected to focus on what they could - the ever-expanding public education system and students who may never go to college. The history workgroup also explicitly mentioned the lack of college access for girls when highlighting the importance of a rigorous historical study in public school.
The impact of the Committee of Ten's report on the classroom, however, is something that is hard to pin down. Krug (1969) theorizes that the Committee described changes that were already happening. A "classics" education was no longer seen as sufficient and schools were adopting a more liberal arts approach to curriculum. Several states had already created high school scopes and sequences that included American history as a stand-alone topic.^7 As the American population expanded, and new high schools were being built, teacher training became increasingly specific (as opposed to general), resulting in the creation of distinct content courses. Additionally, a great deal of the report was taken up by highly detailed proposed courses of study for high school students but a speaker in 1902 at the Association of College and Preparatory Schools of the Middle Colleges said it was not to be found in many schools. (Krug, p. 88)
The piece, however, that most likely helped lock "history class" into the high school schedule was the creation of the Carnegie Unit. In 1905, Andrew Carnegie pledged to pay for college professors' retirement IF the college met his criteria.
must have at least six professors giving their entire time to college and university work, a course of four full years in liberal arts and sciences, and should require for admission, not less than the usual four years of academic or high school preparation, or its equivalent^9
This plan was overseen by Eliot, formerly the chair of the Committee of Ten, who like many of his time, was enamored with "scientific management” and the course credit became fait accompli. Colleges required a certain number of credits for admission and high schools promptly responded by aligning their schedules with credits in the liberal arts and sciences (or risk the possibility of having no students get into college), which included at least one year of American history.
1: Report on the Committee of Ten
2: The First U.S. History Textbooks: Constructing and Disseminating the American Tale in the Nineteenth Century, Joyce, 2015.
4: A Visit to Boston Schools, 1856
5: Tryon, R. M. The Social Sciences as School Subjects, Part XI of the American Historical Association Report of the Commission on the Social Studies. New York: Charles Scribners' Sons, 1935.
6: VanOverbeke, M. The Standardization of American Schooling: Linking Secondary and Higher Education, 1870–1910. Springer, 1935.
7: Krug, Edward August. The shaping of the American high school. Madison: University of Wisconsin Press, 1972.
8: The Course of Study. The School Review Vol. 7, No. 8 (Oct., 1899), pp. 497-501
9: Carnegie Foundation for the Advancement of Teaching. First Annual Report of the Carnegie Foundation for the Advancement of Teaching. New York: Carnegie Foundation for the Advancement of Teaching, 1906.