Fortnite ban backfired spectacularly

So I banned my 12 year old from Fortnite for a month because his grades slipped. Thought it would motivate him. Instead he just plays on his friend's PC at their house after school now and I have zero visibility into what he's doing. Ended up lifting the ban but putting parental controls on our network and we check in on screen time together. Learned my lesson. Sometimes banning stuff just pushes them to hide it better. Anyone else dealt with this?