Kenya's Competency-Based Education (CBE) requires school leaders to steer the pioneer cohort of learners from Junior Secondary School (JSS) to Senior Secondary School (SSS), yet many schools in marginalized counties such as Garissa remain underprepared for the shift. The purpose of this study was to determine how leadership training level influences transition from junior to senior secondary school in Garissa County, Kenya. The study was anchored on transformational leadership theory and supported by Schlossberg's transition adaptation theory. A qualitative, descriptive phenomenological design was adopted. The target population comprised 82 respondents, namely 57 JSS heads, 21 SSS heads and 4 sub-county education officers in Dadaab, Fafi, Balambala and Garissa Township sub-counties, all of whom were targeted through a census. Data were collected through semi-structured interviews and document analysis; 78 participants took part, a response rate of 95%. Data were analyzed thematically using NVivo 14. Only 40% of participants reported having been adequately trained to manage the transition, while 35% reported no such training. The training available was brief, generic and not followed by in-school support, leaving leaders with theoretical knowledge of the CBE but limited practical implementation skill. The proposition that inadequate leadership training constrains effective transition was therefore supported. The study concludes that the deficit lies less in leaders' commitment than in converting that commitment into consistent practice. It recommends practice-embedded leadership development through county-level coaching, professional learning communities, peer mentorship and short certifications in change management and competency-based assessment.