This study presents the features and measured effects of an extra-curriculum program called "4thlabs: science magazine" which targets the promotion of important soft skills such as critical thinking, problem solving, communication and collaboration in high school students. Program's main features include project-based learning and the use of experiential activities. "4thlabs" was attended by 55 students (aged 14-15) of the 4th Junior High School of Aigaleo during school years 2016-2019. The YES 2.0 tool was used to firstly compare "4thlabs" students' program experience with their science courses experience during the same period and secondly with the science courses experience of a non-participants group of 49 students (aged 14-15) attending the same courses. Results show that "4thlabs" has a positive effect in promoting students' collaboration, responsibility, leadership, presenting information, creativity and communication skills. Moreover students enhanced aspects of their problem-solving and emotional regulation abilities. Finally "4thlabs" did not seem to affect diverse peer relationship, effort, goal-setting and time management skills. These results suggest the enhanced educational value and characteristics of targeted extra-curriculum programs in promoting students' soft skills along with science classroom courses.