In many disciplines of STEM education, online experiments (OEs), commonly called remote-controlled experiments, become an emerging practice in technology-enhanced learning because of their many merits perceived in educational research. We recently formulated an innovative, low-cost, and open-source approach to developing new OEs rapidly. It won a gold medal and a special prize in an international innovation and invention competition in 2018. Using this new approach, teachers and students can easily access OEs with a lightweight web browser using any hardware and any operating system without installing additional software or apps. They can observe and/or control the experiments and collect authentic data (over a very short or long time) for further analysis by plotting graphs and/or conducting calculations to obtain important results. Some well-accepted instructional approaches or pedagogies have been integrated into online science/STEM experiments, which can also be aligned with school-based curricula to provide self-contained courseware for students’ online self-regulated learning. In this chapter, we will focus on whether OEs could really and effectively provide the essential elements of experimental learning to ‘school students’ as expected in traditional laboratory work. From our pilot implementation in four Hong Kong (HK) and Mainland China (CHINA) secondary schools with a total of 172 participants, we explored the OE experiences of different experiments and cognitive performance among students from different regions and genders using the conventional mixed methods research and design-based research. Students’ feedback and suggestions for improvement of the OEs were also analysed together with some specific implications for science/STEM education. Copyright © 2022 The Author(s).