Jump Street

Short answer: Undercover as teachers

In 21 Jump Street, the main characters are cops who go undercover as high school students. In the sequel, they go undercover as college students.

By now, they would be much older... and have to go undercover as teachers. Jonah Hill is pushing 40, and Channing Tatum is 43. 

Well, they did high school and college in parts 1 and 2, and Arnold did the cop-undercover-in-kindergarten thing in, um, Kindgergarten Cop. And School of Rock, though not about a cop, was about 5th graders.

What's left? Middle school.

They have have taken down drug dealers, these two hardened cops must now face someone even tougher: 7th and 8th graders. Yes-- 12, 13, and 14-year-olds.

Good luck, guys. 

They went after drug dealers twice, and I don't think you can get comedy out of tweens doing drugs-- it's just too terrifying. But they could be trying to break up a ring of people selling vapes to kids that, unknown to the sellers, are designed to be ultra-addictive. 

Another thing kids to is buy the answers to tests. That in and of itself would not be enough to warrant a police investigation. Unless the answer sheets were being used to transmit a code for plans for, say, a break-in. 

What could a school have that was worth stealing? Let's see-- computers, tech from the robot lab, chemicals from the chem lab, the answer code for that year's SATs. Or it could be some McGuffin hidden in a cup-shaped sports trophy.

It could also be a college-admissions scam like the ones we have seen in the news. 

By the way, the assistant principal did it, and tried to frame the principal along the way.