Looking for some suggestions

I am trying to help out a non-profit children's home with their study lab. They are probably going to continue to have the kids "home schooled" instead of sending them into the school. The problem that I've been fighting is they are not wanting to actually do their school work and browse the web. At first I was able to get a handle on it by using a Raspberry Pi 4 with pihole and setup a block on the URLs. Then they started using anonymous VPNs and proxies to gain access to the internet.

What I am looking for is a solution with what I have on hand with little to no budget. I have a Dell PC and a Raspberry Pi 4 to use for this. It is on a business class cable connection with Comcast which is bridged to a Netgear router.

I do have a list from the online school for a network whitelist.

Any suggestions are greatly appreciated.