In a large city school system with $20$ elementary schools, the school board is considering the

adoption of a new policy that would require elementary students to pass a test in order to be

promoted to the next grade. The PTA wants to find out whether parents agree with this plan.

The following idea for gathering data has been proposed.

Send a survey home with every student and ask parents to fill it out and return it the next day.

What kind of sampling strategy is involved?

lat $($if any$)$ sources of potential bias

do you see