Purpose: Research of mindfulness-based programming/interventions (MBP) for youth has proliferated in recent years; however, heterogeneity of MBP for youth impede determination of optimal programmatic structure across developmental periods. Design/Approach/Methods: Expert MBP scientists and instructors were iteratively surveyed using the Delphi method to assess optimal MBP session structure across developmental periods. Findings: Survey Round 1 defined the participants' perspective of ideal structure across early childhood, middle childhood, and adolescence. In Survey Rounds 2 and 3, participants considered the preceding Round's results (means and SDs) and indicated what they believed was the ideal structure of a single MBP class. Final results following the Round 3 survey indicated that MBP session period should be progressively longer relative to the developmental time period (early childhood mean =20.0 min; middle childhood mean =34.5 min; adolescence mean =50.0 min); that roughly half of a youth MBP session should be dedicated to mindfulness practice; and that progressively more time should be allocated to didactic instruction and discussion, relative to mindfulness practice, as youth become older. Originality/Value: These findings are the first to report expert feedback on the ideal structure of a youth MBP session, and results have significant implications for future youth MBP evaluation, implementation, and curriculum development.