Students with extensive support needs are at risk of demonstrating challenging behavior due to inadequate support of their individual needs or class-wide factors such as low quality of instruction. Students with extensive support needs are also among the students who are most likely to experience aversive interventions and be placed in segregated educational placements. The purpose of this mixed-methods study was to investigate behavior intervention plans (BIPs) written for students with extensive support needs to understand their structural features and technical adequacy, trends across components of plans, and the alignment of the BIP with the student's individualized education program (IEP). We analyzed BIPs that were developed by IEP teams including a teacher candidate enrolled in a master's program, a mentor teacher, or a colleague. We found BIPs were of low technical adequacy with patterns of errors reflecting harmful assumptions about students, lack of operational definitions, and intervention procedures that were not aligned with other components of the plan. BIPs and IEPs were not well-aligned, a finding that reflected overall poor planning for students with extensive support needs. Implications for research and practice are presented with a focus on the critically important nature of effective behavior supports for students with extensive support needs.