For example, which one fits in this context better?
Working as a teacher, she has hands-on experience with suspected drug user students. Working as a teacher, she has first hand experience with suspected drug user students.
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"Hands on" means there is/was a physical interaction. You might have hands-on experience baking cookies, for example.
First hand means "directly." For example, a person who directly worked with drug using students as opposed to someone who read a report the first person wrote about their experience. The person who read the report would be said to have "second hand" knowledge.