These are the appendixes for the report, "Trends and Gaps in Reading Achievement across Kindergarten and Grade 1 in Two Illinois School Districts." This study examined reading achievement data for kindergarten and grade 1 students in two districts in Illinois: District U-46 (Elgin Area Schools) and District 186 (Springfield Public Schools). Drawing on a different reading assessment in each district, the study team documented reading achievement in these two early grades for two kindergarten cohorts (2016/17 for District U-46 and 2017/18 for District 186) and examined disparities in achievement for several student demographic groups. Appendixes in this document include: (1) About the reading achievement assessments; (2) Methods; (3) Supporting analyses; and (4) Other analyses. [For the full report, see ED610445; for the study brief, see ED610448; for the study snapshot, see ED610449.]