They are great research tools and considering that the high school and college years represent somewhere between 6 and 12 per cent of the average persons life, they are worth researching. Besides it is about the most fun family history research one can do.
The first collection of links to free yearbooks was published in 2018 and represented about 4,000 schools.
Recently I have about doubled the number of schools to about 7,800 and have just published the links.
You can find the yearbook link lists in the Yearbooks page, broken down by state and city.
The states that have added over 200 schools in this update include Missouri, New York, Illinois, Indiana, Michigan, Ohio, Pennsylvania, and Texas. Many other states have added a significant number of schools also.
Good Luck and Happy Hunting!