In recent years, there has been an increased recognition of the importance of professional development (PD) programs that prepare grades K-5 teachers to teach computer science (CS) and computational thinking (CT), primarily through integrating these topics into core curriculum. Prior studies using quantitative and qualitative methods have examined outcomes of such PD programs, revealing important aspects to measure when evaluating teacher readiness and concerns about integrating CS and CT into their instruction, including individual capacity, network and resources, and barrier and concerns. The current study aims to fill in the gap of validated instruments to measure teacher readiness and concerns to teach/integrate CS and CT in the K-5 educational context. The instrument was developed based on existing validated measures and adapted for the K-5 teacher population. Pre-survey data from 641 K-5 teachers trained to integrate CS and CT into their instruction was used to validate the instrument. Internal reliability and exploratory factor analysis (EFA) were conducted on two subscales: readiness and concern to integrate CS/CT. Results suggested satisfactory psychometric properties for both subscales overall, but suggested the removal of one item on each subscale to further improve internal reliability and factor structure. Pearson correlation results suggested the readiness and concern subscales were moderately correlated (r=-0.38), indicating readiness and concern to be two correlated but separate aspects in teachers’ preparedness to integrate CS and CT in K-5 classrooms. The development and validation of this instrument provides a reliable and valuable tool to assess future PD program outcomes in K-5 CS education.