Key study: Charlton et al (2000)

Aim: to see whether the arrival of broadcast television changed young children's pro-social and antisocial behaviour.
Setting: St Helena, a small, remote British island in the South Atlantic, which did not have broadcast TV until the mid-1990s. This made it a natural experiment: the researchers did not introduce TV, it happened naturally.
Participants: children aged about 3 to 8 at the island's schools.

Children were video-recorded during free play in school playgrounds, shortly before TV arrived and again in the years after (up to about five years later).
The recordings were coded using a checklist of pro-social behaviours (such as helping or sharing) and antisocial behaviours (such as hitting or pushing). Two coders checked each other's coding for inter-rater reliability.
Results: there was very little change in behaviour after TV arrived. Most comparisons showed no significant difference, and the few that did were mixed. Boys showed more antisocial acts than girls, both before and after TV.

Conclusion: TV alone did not make these children more aggressive. The close, caring community, with strong family and school supervision, may have protected them.
Strengths: high ecological validity: real children in a real playground. It was longitudinal (over several years). Video recordings could be checked by more than one coder, improving reliability.
Weaknesses: St Helena is unusual (small and close-knit), so results may not generalise to larger cities. As a natural experiment, other variables could not be controlled. How much TV each child watched was not measured.