If you are absolutely determined to make a lawyer of yourself the thing is more than half done already

From Increasingly Competitive College Admissions: Much More Than You Wanted to Know by Scott Alexander.

Or suppose you wanted to be a lawyer. The typical method was called “reading law”, which meant you read some law textbooks, served an apprenticeship with a practicing lawyer, and then started calling yourself a lawyer (in some states you also needed a letter from a court testifying to your “good moral character”). Honestly the part where you apprenticed with an practicing lawyer was more like a good idea than a requirement. It’s not completely clear to me that you needed to do anything other than read enough law textbooks to feel comfortable lawyering, and then go lawyer. Most lawyers did not have a college degree.

Abraham Lincoln, a lawyer himself, advised a law student:

If you are absolutely determined to make a lawyer of yourself the thing is more than half done already. It is a small matter whether you read with any one or not. I did not read with any one. Get the books and read and study them in their every feature, and that is the main thing. It is no consequence to be in a large town while you are reading. I read at New Salem, which never had three hundred people in it. The books and your capacity for understanding them are just the same in all places.

Levi Woodbury, the 30th US Supreme Court Justice (appointed 1846), was the first to attend any kind of formal law school. James Byrnes, the 81st Supreme Court Justice (appointed 1941), was the last not to attend law school. It’s apparently still technically possible in four states (including California) to become a lawyer by reading law, but it’s rare and not very encouraged.