Data scientists benefit from collaboration: data scientists work across disciplines with a variety of stakeholders in practice [1]; data scientists collaborate between the team to improve work efficiency [2]; citizen data scientists collaborate in an open source manner to collectively explore topics of shared interests [3], [4].However, collaboration in data science is often hard. Since data science is highly exploratory [5], the artifact and analysis often iterate fast. It is difficult to maintain a shared understanding across various collaborators. On the other hand, tools like computational notebooks provide a convenient approach for data scientists to run, document, and share analysis in a storytelling way [6]. It satisfies the basic collaboration needs for data scientists to communicate and iterate on each other's work. However, such benefits are rudimentary. There are still many open-ended questions about how to improve the collaboration experience by designing better collaborative data science tools. For example, data scientists often neglect to keep updated documentation during rapid exploration, which results in computational notebooks that are messy and difficult to read [7]; without strategic planning, working together in a shared notebook may block each other's work.My research draws upon human-centered design techniques to identify barriers in real-world data science programming practices, and explore the design space of collaborative data science environments through tool-building. In this paper, I will first review our prior work on understanding how data scientists use computational notebooks for collaboration [8]. Through a mixed-method study, we found that working on the synchronous notebooks improves collaboration by creating a shared context, encouraging more exploration, and reducing communication costs. We also identified several challenges with the synchronous notebook editing tools such as producing messy and less organized notebooks, causing conflict editing without strategic planning.Inspired by the study results as well as related work, we then developed a series of prototypes that aim to help data scientists handle off work during collaboration: 1) a prototype that captures the contextual links between messages and notebook elements [9]; 2) a set of automatic approaches