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 lowest quartile had only reached average 4th-grade level because they had such a small vocabulary in 2nd grade. There is evidence that words are learned in roughly the same order. The implications of these findings suggest (a) that greater efforts should be made to foster vocabulary acquisition in the primary years and (b) that a rough vocabulary curriculum sequence can be identified for the elementary years.