The internship is a critical part of graduate training and often the only opportunity to receive on-site clinical supervision during school psychology practice. Nonetheless, the process of pairing interns with field supervisors is not standardized and sometimes relies on factors such as logistics and supervisor credentials rather than a consideration of interpersonal variables that could optimize the internship experience. Related fields have found mixed evidence for a relationship between personality similarity within a supervisory dyad and outcomes such as a strong supervisory relationship, satisfaction with supervision, and supervisee effectiveness. This study examined the influence of personality similarity on ratings of supervisory working alliance, supervision satisfaction, and intern work readiness. This study also evaluated the predictive power of personality, supervisory working alliance, and systemic factors on intern work readiness and supervision satisfaction. Lastly, this study assessed the development of the supervisory working alliance and intern work readiness over time. Twenty-six dyads were recruited for participation in this study, including 24 practicing school psychologists serving as field supervisors and 26 school psychology interns. Data collection occurred at the midpoint and end of the internship year. Participants completed a demographic questionnaire, personality inventory, and measures of supervisory working alliance, supervision satisfaction, supervisee work readiness, and systemic factors. Results indicated that personality similarity among supervisors and interns is not related to supervisory working alliance, supervision satisfaction, or supervisee work readiness. However, supervisor ratings of supervisory working alliance were predictive of intern work readiness, and intern ratings of supervisory working alliance were predictive of supervision satisfaction. Systemic factors were not predictive of intern work readiness or supervision satisfaction. For supervisors, the supervisory working alliance significantly decreased over time, while intern ratings remained consistent from midyear to the end of the year. Intern development from midyear to the end of year could not be determined due to low scale reliability. Future studies should further examine factors that contribute to the supervisory working alliance and validate measures specific to the school context. More research is needed to establish the conditions and interpersonal characteristics that enable an optimal internship experience for both supervisors and supervisees in school psychology.