The Standards for Mathematical Practice (SMPs; CCSSI, 2010) describe mathematical behaviors and habits that students should express during mathematics instruction. Teacher candidates should have knowledge about the SMPs and their implications for mathematical instruction. This study aims to share the validity evidence for interpretations of outcomes from the SMP-Knowledge Assessment (KA) as a measure of teacher cadidates' knowledge related to the SMPs. Knowledge of the SMPs involves both mathematics content and a knowledge of students' behaviors as they engage with mathematics. The SMPs are an important part of teacher candidates growth in their knowledge for teaching. As such, teacher educators and researchers need robust ways of monitoring and measuring teacher candidates learning of growth in their knowledge of the SMPs. The SMP-KA is an instrument to measure K-12 teacher candidates' complex knowledge of the SMPs. The gathering of validity evidence with teacher candidates for the SMP-KA followed validation standards (AERA, APA, & NCME, 2014). The results provide sufficient validity evidence to support the use of the SMP-KA to assess teacher candidates' knowledge of the SMPs. We encourage other instrument developers to report validity evidence with the teacher candidate population.