This research study examined the relationship between years of traditional classroom teaching experience and teaching in school library instructional environments. Data for the study emerged from formal observations of MLS candidates' practicum teaching in school libraries. Participants in the study were examined based on the following levels of teaching experience: No Experience, Novice (1-3 years), Experienced (4-9 years), and Experienced Plus (10 plus years). Twenty planning, instruction, and reflection competencies were examined. One assessed competency, New Content Modeled, yielded increasingly better performance across levels of experience beginning in the fourth year of experience. Increasingly better performance was not noted among the nineteen other competencies assessed across all experience levels. Lesser-experienced candidates tended to score higher on planning proficiencies than did more-experienced candidates. No significant differences were noted across all competencies between candidates with no teaching experience and candidates who were teaching novices. In the transition from the Novice to Experienced levels, a significant theme emerged as thirteen significant paired comparisons in planning, instruction, and reflection competencies were noted in this critical transition period. Study findings reinforced "the simple assumption that more teacher experience is better requires greater nuance; experience effects are complex and depend on a number of factors" (Rice 2010, 1).