There is additional evidence regarding dose–response from a survey conducted for the Metropolitan Life Insurance Company in 1988. This survey of 4,738 students in grades 3 through 12 in 199 public schools revealed that as the years of health instruction increased, students' health-related knowledge and healthy habits increased. With one year of health instruction, 43 percent of the students drank alcohol ''sometimes or more often," a level that decreased to 33 percent for students who had received three years of health instruction. With only one year of health instruction, 13 percent of the students had taken drugs, compared with only 6 percent who had received three years of health instruction. In regard to exercising outside of the school, 80 percent of the students who had three years of health instruction did so, but only 72 percent of those who had one year of instruction exercised outside of school (Harris, 1988).

Duration, Sequence, and Timing of Health Education

Two other aspects of dose include intensity of programming (i.e., concentrated versus dispersed) and booster treatments. With regard to the former, Botvin and colleagues (1983) found that students who received a substance use education program several times a week for 4 to 6 weeks (a "concentrated" format) showed stronger treatment effects than youth receiving the program once a week for 12 weeks (a "dispersed" format). Additionally, in two separate studies, students receiving booster sessions following a year of primary intervention showed larger and more sustained behavior effects than youth receiving only the initial intervention (Botvin et al., 1983; Botvin et al., 1995). Taken together, these findings suggest that the greater the intensity and duration of health education programming, the greater is the effect. It is important to note that "increased dose" can include two elements. The first relates to the number of lessons contained in a curriculum; the second is a function of implementation fidelity on the part of classroom teachers. Thus, a complex, non-user-friendly health education program containing many lessons may, due to low teacher implementation, result in a lower dose than will a more user-friendly program containing fewer lessons.

With regard to specific policy recommendations, there are insufficient data to delineate a requisite number of lessons across content areas and grades. There is, however, some evidence to suggest that at least 10 to 15 initial lessons, plus 8 to 15 booster sessions in subsequent years, are required to produce lasting behavioral effects (Botvin et al., 1983, 1995; Connell et al., 1985). These data, however, are derived primarily from substance use prevention studies of middle school youth. Little is known about the requisite intensity and duration of programming for other content areas or other age groups. It is also unclear to what extent general life

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