Wright and Neuman (2015) found vocabulary instruction to be lacking:

“In our study of 55 kindergarten classrooms, for example, we found that although teachers provided more than eight of these word explanations per day, they were rarely, if ever, repeated more than once.”

Marulis & Neuman (2010) – 67 studies, 60% in PK, 40% K: EF .88 (.71 on standardized): 

“Programs that used explicit instruction deliberately either through explanation of words or key examples were associated with larger effect sizes...”

Chall, et al, 1990 Low vocabulary by 3rd grade = declining reading comprehension scores in later years (“4th Grade Slump”) .

Vocabulary researchers have identified key elements which have been effective in increasing children’s vocabulary knowledge (Graves, 2016; Silverman & Hartranft, 2015). Patrick Manyak (Manyak & Manyak, 2021; Manyak et al., 2021), a former University of Wyoming professor and a current elementary school principal in California, conducted multiple formative experiments, the VALE research studies. He found three elements, quality, quantity, and strategy dimensions of vocabulary instruction to be effective at increasing K-5 students vocabulary. Ellen Kappus conducted two studies with him in second-grade dual immersion and Kindergarten. Outcomes from these two VALE studies, one involving six second-grade dual-immersion classes (VALE-DI) and one involving 13 kindergarten classes (VALE-K), demonstrate the highly effective nature of long-term, multifaceted vocabulary instruction guided by the VALE framework.