OP here. I appreciate all the advice you guys gave, and I noticed a few of you mentioned gold. I ended up putting all 20 dollars into SSRI (silver standard resources) and bought 3 shares of it. I looked at several mining companies, and I noticed that throughout history these mining companies seemed to do better when the economy slowed down. So far my shares have increased by an alarming $1!
And I'll answer the question as to why he's doing this. He wants us to realize it is basically a gamble, and it is not a get rich quick scheme. You hear success stories all the time or someone who made it big overnight, but it's just too risky. My teacher actually made 15 grand off of a weed investment in Colorado right as it became legal, but even he will admit he was lucky.
And to address the question about the transaction fees, he is giving us $20 to spend freely on shares, and on to of that he is covering the transaction fee. All in all he has put in about $300 or more into this, and it's honestly one of the most enjoyable projects I've done so far.