Throw some Cheerios or fruit loops in the toilet because then they have something to aim for make it like a game and it's easier to train them then
It depends on how they are being taught. My son started prek 3 and he learned in 2 days I tried before he went to school and my parents never continued to teach him when they had him. He learned pee never poop since he started school
The Dr. Becky guide worked really well for my son. It was free when I downloaded it.