Purpose
The purpose of this study is to identify which elements of team-based learning (TBL) are the most difficult to implement in the pre-clerkship medical curriculum. TBL is widely used in medical schools, yet the literature shows that many facilitators do not implement all the identified essential features of TBL. This limits research and practice related to TBL.

Methods
Data was collected via a review of the TBL literature over the past twenty years, along with one-on-one interviews with 17 TBL trainer consultants from US medical schools.

Results
TBL trainer-consultants identified the 4S application exercise and peer review as the two most difficult elements to implement in the pre-clerkship curriculum. This was also apparent in the literature review, where several studies struggled to implement the peer review process and use the 4S model during the application exercise. Consultants identified the peer review process as difficult because most schools do not supply the resources or time required for implementation, and faculty do not perceive the time to participate in the process as valuable. For the use of the 4S model, faculty understand the value of the exercise but describe it as difficult because it takes time and practice to create a good case that promotes student discussion.

Conclusion
This study identified which elements of TBL are the most difficult for faculty to implement when using TBL in their curriculum. At the institutional and department level, faculty need to be provided with the time and resources to successfully implement these two critical elements of TBL. For example, faculty should be provided with dedicated time to develop 4S application exercises and attend TBL workshops, and there should be staff support for the peer review process.