Clinical teaching is vital for preservice teacher (PST) development, yet field supervisors' roles are understudied. This study analyzes over 11,000 supervisor evaluations and PST reflections from a Texas teacher preparation program using large language models to extract measures of feedback quality and content. Supervisor feedback often lacks key quality indicators: less than half of evaluations include areas for improvement or actionable next steps. Supervisors most frequently identify classroom management as needing improvement, whereas PST reflections more often focus on lesson planning. PSTs receiving classroom management feedback receive lower evaluation scores and are less likely to return to their placement schools as in-service teachers. These findings highlight an opportunity to improve supervisor feedback and better support PST growth during clinical teaching.