The purpose of the present study is to investigate homogeneity of reading passages in the National Assessment of Educational Achievement(NAEA) English Tests from three years (2015-2017) in terms of their readability influenced by a combination of diverse textual characteristics. In order to conduct a quantitative analysis, this study utilized 12 benchmarks of text analysis provided by a web-based text analysis tool, Coh-Metrix. The general framework for the analysis involving the intentional selection of 12 indices was largely motivated by a previous study that dealt with a similar topic. Coh-Metrix offered numeric outputs for the following selected categories of text analysis: (a) basic counts (2 indices), (b) lexical diversity and frequency value (4 indices), (c) syntactic complexity (2 indices) (d) cohesion (4 indices). Each output from the Coh-Metrix’ computations was then statistically processed to test any mean differences among the reading texts in the NAEA English tests from three years on scales of the 12 indices. It was found that reading passages were homogeneous in most of the indices enumerated above. However, they demonstrated statistically significant differences in 2 indices of DESSL from the basic count and SYNLE from the syntactic complexity, which respectively refers to the mean length of sentences used in the reading texts and the number of words placed before a main verb. The pedagogical implications will be discussed.