BACKGROUND: The purpose of this study was to determine the effectiveness of Ready for Recess, an elementary school recess intervention targeting staff training (ST) or providing recreational equipment (EQ) separately, and the combination (EQ+ST) on physical activity (PA). METHODS: Participants were children attending 1 of 12 elementary schools (grades 3rd-6th) included in the study. Separate analytical models were used to evaluate the effects of the intervention conditions on children’s accelerometry and direct observation derived PA measures.  RESULTS: Boys and girls were measured using accelerometry (n = 667). Boys in EQ+ST increased their MVPA by 14.1% while ST decreased their MVPA by -13.5%. Girls in ST decreased their MVPA by -11.4%. Neither boys nor girls in EQ increased their time spent in MVPA. A total of 523 (boys) and 559 (girls) observations were collected. For boys’ and girls’ sedentary and vigorous activity there were no significant main effects for treatment condition, time, or treatment condition-by-time effects. CONCLUSIONS: Environmental modifications are only as strong as the staff that implements them. Supervision, if not interactive, may be detrimental to PA participation, especially in girls. Research related to staff training for encouragement and promotion of PA coupled with appropriate use of equipment during recess is warranted.