Michalopoulou Μ., Dimopoulou Ε., Zetou Ε. and Kourtessis Θ. 2007. The Effect of Contextual Interference and Variability of Practice on Learning Volleyball Skills in 9th Grade of Greek High School. Inquiries in Physical Education and Sport. 5, 1 (Apr. 2007), 10–18. DOI:https://doi.org/10.26253/heal.uth.ojs.ispe.2007.1174.