Kevin could divide his neighborhood into five homogeneous groups and choose one group at random to survey houses within

Kevin could survey every third house in his neighborhood

Kevin could survey five houses at random on every single street in his neighborhood

Kevin could number each house from 1 to 300 and then randomly select 120 houses to survey using a random number generator

Kevin could divide his neighborhood into five different groups and select 25 houses at random from each group to survey

Randomly select an elementary school from the entire list of elementary schools in the country

Find a local elementary school and perform the experiment there.

Find a list of all elementary schools in the state and then only look at schools with weak math programs before selecting which schools to run the experiment in.

Select a "cluster" of schools in a local area.

Randomly select an elementary school in the country and ask the principal to recommend other schools that would be interested in participating.