As for Americans in their early 20s, the National Assessment of Education Progress found in 1985 that 6 percent could not read as well as the average 4th grader and 20 percent could not read as well as an 8th grader ("20% of Young Americans," 1986). Therefore, it seems reasonable to assume that a significant number of parents in these school programs for educationally disadvantaged children are unable to read the communications sent to them by the schools.
Mavrogenes, N. A. (1988). Readability and Parent Communications: Can Parents Understand What Schools Write to Them?. Reading Horizons, 29 (1). Retrieved from http://scholarworks.wmich.edu/reading_horizons/vol29/iss1/1