Psychometric test validation question We are trying to validate a test for young children using IRT analyses (rasch/2pl). Models do not converge due to a floor effect. Teachers also took this assessment. Would it skew results if i combined teacher data with the child data and re-ran the models even though the assessment was designed specifically for young children? Could you publish a paper and claim validity evidence for a test with combined data like this?

You don't usually test for validity using IRT. Validity is whether a test measures what you propose that it measures.
If you have a floor effect (for children), this means that the test is not sensitive at detecting differences between high and low performing children. If you add teachers, this will just tell you whether the test is good at differentiating between teachers and children - I don't think you care about that, and I don't think it's what you plan to use the test for, so I wouldn't.
