Science is taught at the pre-primary level to foster scientific skills, essential for learning science at other levels of education. There is evidence that children are deficient in the scientific skills of observation, classification, communication, measurement, prediction and inference. This problem has been attributed to teachers' non-use of sciencing activities for children. This study was, therefore, carried out to determine the effects of sciencing activities (formal and informal) on pre-primary school children's scientific skills in Ibadan, Nigeria. The pretest-posttest control group quasi-experimental design was adopted. Three public primary schools were purposively selected from three Local Government Areas in Ibadan, Nigeria. An intact pre-primary class was used from each school, and randomly assigned to Formal Sciencing (17), Informal Sciencing (19) and Control (24) groups. Science Process Skills Rating Scale (r=0.73) was used to measure the scientific skills of children before and after exposure to sciencing activities. Data was analysed using descriptive statistics, Analysis of covariance and Scheffe post-hoc test. There were significant main effects of treatment on children's scientific skills (F[subscript (2, 57)]=47.72; partial [eta][superscript 2]=0.65). Among the recommendations made was that sciencing activities should be adopted by pre-primary teachers to foster scientific skills of pre-primary school children.