This study investigated the impact of outdoor educational activities on pupils' knowledge of some environmental issues and problems. A pretest, posttest, control group, quasi-experimental design was adopted for the study. Four hundred and eighty primary 5 pupils from 12 randomly selected primary schools in Ibadan, Nigeria, constituted the subjects for the study. The instrument used was an Environmental Knowledge Test (r= 0.86). Data collected were analyzed using descriptive statistics of frequency counts, means and standard deviation, and inferential statistics of ANCOVA. Treatment had significant main effect on pupils' environmental knowledge (F[subscript (1,471)]= 137.37; p less than 0.05). Pupils exposed to outdoor educational activities with discussion performed better in knowledge ([X-bar] = 19.59; SD = 1.78). Outdoor educational activities with discussion proved more effective at improving pupils' knowledge of environmental issues and problems. (Contains 3 tables and 1 figure.)