In Simple Words
When two completely different groups of students use the exact same school building at different times of day—one group leaving before the second group arrives—the physical building is shared, but the social environments are totally separated by time, functioning like two completely separate schools under one roof.
Research question
In developing nations, public schools often run multiple daily student shifts, creating potential confusion over whether morning and afternoon cohorts interact enough to contaminate experimental control groups.
Participants
N = 69 public secondary schools across 21 Colombian cities, including 13 dual-shift school buildings.
Study Design
Methodological unit definition treating non-overlapping morning and afternoon school shifts as distinct independent schools due to strict shift assignment and zero cross-shift student contact.
Results
Validated shift-level experimental independence across 13 multi-shift facilities without cross-shift contamination or social interaction overlap.
Takeaway
Treat non-overlapping time shifts in shared physical facilities as distinct, independent sampling units when conducting field evaluations in multi-shift public infrastructure.