This paper describes an Online Teaching Lab model that incorporates elements of lesson study and studio model for teacher learning. We focus on changes in design and facilitation decisions of two specific Online Teaching Labs and study differences in teachers' verbal and written responses to better understand how the process supports teacher learning. Middle grades mathematics teachers took part in the Online Teaching Labs. Data included video recordings of professional development team meetings, lesson implementation, Online Teaching Labsi and teachers' written work on 'Capture Sheets.' Data were analysed based on observable behaviours we intended participating teachers would enact. We found a relationship between the intentional changes facilitators made from the first to second Online Teaching Lab and teacher responses. Facilitators made more explicit mention of the learning goals, increased opportunities for teacher discussion, and included varied video clips. As compared to teachers in the first iteration, teachers in the second Online Teaching Lab more frequently identified teacher discourse moves related to engagement and cognitive demand of tasks and identified connections between teacher pedagogy, student strategies, and mathematical goals. The design, implementation, and outcomes are novel because the model includes features of lesson study and studio model through an online medium.