Science educators have suggested many benefits that accrue from engaging students in experimental activities, therefore, experimental work has a long and distinctive role in chemistry curriculum since. The presented empirical study focuses on the valuation of effectiveness of different forms of experimental work - students' hands-on experimental work vs teacher's lecture demonstration - from the viewpoint of the quality of content knowledge acquisition and knowledge retention in teaching primary school chemistry. 106 primary school students (age 14-15 years) participated in the study. The data was collected via pre- and post- test protocol and two delayed post tests. Additionally 16 students selected from the sample were interviewed. The results indicate that students' content knowledge gained through teacher's demonstration of experiment is better and better knowledge retention takes place in comparison to students' knowledge gained through students' hands-on experimental work. However, most of the inteviewed students stated that they prefered conducting of experiments by themselves in comparison to observation of teacher's demonstration.