Disable Application During Class
Parental controls allows you to exert more control over standard accounts and could restrict that app easily for you. In practice, I prefer other levers.

Whether it's worth the time to setup vs. getting out and moving around the class (or having an assistant sit in the back of the class and keep an eye on screens) is debatable.

Assuming you don't already have an MDM/imaging workflow and this is just a bunch of computers that you go to one by one to manage I'd just move the Minecraft app outside the student directory and set up ssh keys / use Apple Remote Desktop to place a link to the app in each user's ~/Applications folder if and when you want them playing that app or game.

That method is very useful for other problems, has low cost of tools and might be a nice introduction to things like munki/autopkg/etc... for improving the management of this lab of Macs.

You can also leverage Apple Remote Desktop to monitor all the screens in the classroom. I'd take an old iPad and use Duet Display so that my Main screen(s) were devoted to the work I was doing as opposed to cycling through screens to see who needed their screen locked due to minecraft violations.