Estimating root word vocabulary growth in normative and advantaged populations: Evidence for a common sequence of vocabulary acquisition.

Root word vocabulary was studied in 2 normative samples (English-speaking, wide socioeconomic range) and in an advantaged sample. The authors estimated that in 2nd grade, the mean normative vocabulary was 5,200 root words, increasing to approximately 8,400 root words by 5th grade. During grades 3-5, the lowest quartile added about 3 root words a day, whereas the highest quartile added about 2.3 words a day. However, by 5th grade, children in the...