Sample size (or number of clusters) by treatment arms
750 students in control group.
Remaining students will be divided evenly between cells defined by encouragement intervention, communication medium, and frequency/timing.
The encouragement interventions are:
1. academic coaching
2. Economics peer tutoring
3. extra practice
The communication media are:
2. text message
3. email, with lottery incentive
4. text message, with lottery incentive
The frequency/timing combinations during the 10 weeks of the term are:
1. Week 3
2. Week 6
3. Week 9
4. Weeks 3/6
5. Weeks 3/9
6. Weeks 6/9
7. Weeks 3/6/9
Within the subsample of treated students who do not provide a phone number, there are thus 42 possible combinations of treatment characteristics (3 messages x 2 incentives x 7 frequency/timing combinations). Within the subsample of treated students who provide a phone number, these 42 combinations exist for both media, leaving 84 possible combinations. We will divide students as evenly as possible among these treatments, though actual cell sizes may vary due to the large number of treatment combinations.