As science and technology create an ecosystem that is becoming increasingly more knowledge-intensive, complex, and interconnected, the next generation science standards include systems thinking and systems modeling among 21st skills that should be fostered. We examined the effect of an online cross-disciplinary learning process on the development of systems thinking and modeling skills among engineering students and engineering and science teachers. The study, which used quantitative and qualitative tools, included 55 participants who performed four food-related learning assignments and created conceptual models in Object-Process Methodology. Their responses to online assignments were analyzed along with their perceptions, captured via a reflection questionnaire. The online learning process in this study effectively enhanced systems thinking and modeling skills of all learners, including those with no relevant background. One main conclusion that extends beyond the online learning was that imparting the basics of systems thinking and conceptual modeling skills can be achieved even within a short period of time--less than one semester. The contribution of the study is the formation of theoretical and practical frameworks for the integration of an cross-disciplinary model-based systems engineering online assignments into engineering and science curricula.