The aim of this study was to investigate whether soccer free kick training improves the knuckle ball technique of adolescent and adult male soccer players after a three week training period using either internal or external focus of attention instructions. Much evidence has been gathered in the literature showing that an external focus of attention (i.e., focus on the movement effects) is more effective than an internal focus (i.e., focus on the movements themselves) during learning. In the present study, 56 soccer players (20 adolescents and 36 adults) completed a free kick training program for which attentional focus (internal vs. external) was manipulated. Results indicated that the external focus group showed greater improvements compared to the internal focus group. These findings therefore provide further support for the advantages of external focus of attention instructions during skill acquisition and further show that this remains true for prolonged training periods.