Learning-by-doing (LBD) in experimental physics teaching is crucial for engaging students in the scientific process and improving their understanding of physics laws. Hands-on experimentation allows learners to experience natural phenomena in their actual environment, the natural world. This work presents the implementation of two laboratory units on fluids, targeting students and STEM educators. One hundred eighty-eight primary and secondary science teachers in Greece attended the two subjects on water and air as part of a MOOC for STEM experiments. Additionally, 82 K-2 and K-5 students participated in some proposed hands-on experiments. The results of both studies are presented in detail, aiming to propose improvements for experimental teaching at all levels of science education. Data was collected using qualitative and quantitative research methods. The selected data was analyzed to determine the level of comprehension of physics laws with a special focus on fluid mechanics. According to the present research, the proposed method of LBD, hands-on experimentation, provides excellent learning outcomes. It leads to a satisfactory understanding of fundamental laws and principles regarding fluids –and their respective engineering applications– regardless of the participants’ cognitive backgrounds.