In this article we describe and evaluate processes utilized to develop an online learning module on mathematical modelling for pre-service teachers. The module development process involved a range of professionals working within the STEM disciplines including mathematics and science educators, mathematicians, scientists, in-service and pre-service secondary mathematics teachers. Development of the module was underpinned by Bybee's five E's enquiry-based approach and Goos et al.'s twenty-first century numeracy model. Module evaluation data is examined in relation to the quality of pre-service teachers' learning experiences and interview data from the study is analysed through the lens of 'boundary crossing'. While the evaluation of the module was generally positive, aspects that required improvement were also identified including more meaningful inclusion of pre-service teachers and other stakeholders in the development process.