19 y/o seeking investment and finance help

I am a 19 y/o male going to community college for an associates degree in environmental science. During the summer I work enough to pay off a single semester in full-- i currently have close to $4000 in a checking account. I want to find the best way to invest this money and make it grow while I am at school.

I fund my schooling through a $3500 direct unsub stanford loan. Some people say "paying down debt" is the best investment. Would it be wise to pay off this loan fully and avoid cost added by interest and time?

If I was to pay off the school loan, is paying it off in full the best method?