The demographics of teachers in the United States have changed significantly over the last 100 years. Here are a few key ways in which teacher demographics have evolved:

Gender: In the early 20th century, the majority of teachers were women. However, as more men entered the teaching profession, the gender balance has shifted. Today, the teaching profession is split roughly evenly between men and women.

Race: Historically, the teaching profession has been predominantly white. However, over the last several decades, the number of teachers of color has increased, particularly in urban and minority-majority schools. This is a result of a growing minority population in the United States and policies to diversify the teaching workforce.

Age: The average age of teachers has also changed over time. In the early 20th century, many teachers were in their 20s or 30s. However, as the profession has become more established and stable, the average age of teachers has risen, with many teachers now in their 40s and 50s.

Education level: In the early 20th century, many teachers held only a high school diploma or teaching certificate. However, as the teaching profession has become more professionalized, the education level of teachers has risen, with most teachers now holding at least a bachelor's degree.

Specialization: In the early 20th century, most teachers were generalists who taught a variety of subjects. However, in recent years, there has been a trend towards more specialized teachers, particularly in subjects such as math, science, and special education.

Career Path: As the profession has become more established, the career path of teachers has changed. Teachers are now more likely to stay in the profession for their entire career and progress through the ranks of the profession, rather than moving into other careers.

Overall, the demographics of teachers have changed over the last 100 years, with a more diverse, older, and better-educated teaching force, with more specialized teachers, and with a more defined career path. These changes reflect broader societal changes, and the evolution of the teaching profession itself.