Field practice is seen as vital for building student teachers' skills and confidence in their abilities to engage in teaching practices. Previous research evaluates student teachers' self-efficacy with instruments for fully trained teachers in real school contexts, risking responses that inaccurately reflect or even misrepresent their true self-efficacy for teaching practices. The present study introduces the Practice Self-Efficacy Questionnaire (PSEQ), a targeted instrument to measure student teachers' self-efficacy in field practice and examines its validity. The study utilizes qualitative data from various stakeholders to develop a 40-item multidimensional instrument measuring seven practice self-efficacy dimensions. Item analyses by Rasch models were conducted with a sample of 303 year-one student teachers, a third of which had prior field practice experience. Two subscales fitted the pure Rasch model, two subscales each had three locally dependent items, two subscales had two locally dependent items, and the last subscale had one item that functioned differentially in relation to prior teaching experience. Criterion validity related to prior teaching experience confirmed expectations, showing that more experienced students scored higher across all sub-constructs. Targeting of the subscales to the study population was good to excellent, while reliability was less than satisfactory for two of the subscales.