If the female is attractive the verdict is usually not guilty, but if the jury does find them guilty the judge will give them probation and a short jail sentence. It doesn’t matter which sex the child is. The same rules do not apply if the adult is a male. He’s going to jail for a long time (unless he’s in some state like Vermont.)
In the state of Washington a teacher having sex with a H.S. student that is 18 is not a crime.