Selecting assessments for adults who struggle with reading can be difficult because few literacy measures used by reading researchers have been normed on this population, leaving uncertainty regarding the validity of these tests for adult learners. This study focused on the performance of 116 adults reading between the 3rd and 8th grade levels on a selection of reading fluency tests and other reading tests. The study examined the convergent and discriminant validity of the measures, taking into consideration the trait and method represented in the assessments in order to analyze how these reading fluency tests (Test of Silent Word Reading Fluency, Test of Silent Contextual Reading Fluency, Test of Word Reading Efficiency, Woodcock Johnson Reading Fluency) function when administered to a sample for whom they were not designed. The results suggest that there may be inconsistent patterns in the convergent and discriminant validity of these measures with this group of adult learners. Based on the findings of this study, suggestions are made for assessment selection for this population.