Chronic absence is a nationwide problem, even among young students. Those with poor attendance are more likely to face challenges later in school and in life. This study tested four versions of an adaptive text messaging strategy to see which, if any, would reduce chronic absence among 26,000 elementary school students. The study compared two approaches to basic messaging and two approaches to intensified messaging, to learn how a texting strategy might work best. Students in the messaging groups were compared to students whose parents received no messages to rigorously assess whether the messaging improved attendance and achievement. This report presents the appendices to the study: (1) More on the Text Messaging Strategy; (2) More on the Study Design; (3) Detailed Impact and Implementation Findings; and (4) Cost and Cost Effectiveness Analyses. [For the full report "Can Texting Parents Improve Attendance in Elementary School? A Test of an Adaptive Messaging Strategy. Evaluation Report. NCEE 2020-006," see ED607613. For the study highlights "Can Texting Parents Improve Attendance in Elementary School? A Test of an Adaptive Messaging Strategy. Study Highlights. NCEE 2020-006," see ED607615.]