The authors explored the credibility of using informal reading inventories and writing samples for 138 students (K-4) to evaluate the effectiveness of a summer literacy program. Running Records (a measure of a child's reading level) and teacher experience during daily reading instruction were used to estimate the reliability of the more formal Developmental Reading Assessment scores. Training of scorers was used to increase the reliability of writing scores; a second scoring was used to estimate the reliability of the scores. The results suggested that with minimal modifications to administration and scoring procedures, scores from both reading inventories and writing samples can be a dependable source of data for teachers, administrators, and policy makers. This result is significant because it suggests that formative literacy assessments can be reliably used instead of standardized multiple-choice tests to make more credible summative decisions without taking time away from instruction, and can truly match curriculum, instruction, and assessment. (Contains 2 tables.)