Asthma is one of the most common chronic conditions among children in the United States. In 2009, an estimated 10.2 million US children (9.6%) had diagnosed asthma (1). In California in 2007, approximately 1.4 million children (15.4%) had diagnosed asthma (2). Asthma is also one of the leading causes of school absenteeism (3). In 2008, asthma accounted for an estimated 14.4 million lost days of school among children nationally (4). In California, school-aged children missed approximately 1.6 million days of school because of asthma in 2007 (2). School absences have consistently been associated with worse academic performance (5-7). Students who miss more school score lower on standardized tests in both reading and math (6,7) and are more likely to drop out before graduating from high school (5,8). Students with asthma are absent from school more than those without asthma (9). As a result, students with asthma may be more likely to experience the poor academic outcomes associated with increased absenteeism.

Students from families with lower socioeconomic status (SES) miss more school (10,11). However, few studies have examined whether school absenteeism is related to the school-level concentration of low-income students, independent of family income. Rothman found that having a higher percentage of students from low-SES families was associated with a higher school absence rate (10). If school-level factors are related to absenteeism, school-level interventions may help to reduce absenteeism. School absence due to illness such as asthma not only affects individual students but also can affect other students who attend the same schools. In California, school districts are funded on the basis of daily attendance (12,13). When students miss school, funding for their school is reduced. Because low-income school children are more likely to have severe asthma and to miss school because of asthma, schools with a large proportion of low-income students may be disproportionately affected by absences due to asthma (2). As a result, school-level interventions can affect not only the targeted students but also other students attending the same schools (14).

Examining whether school absenteeism is related to indicators of school-level disadvantage can inform the development of school-level interventions to reduce asthma-related school absences. We tested the hypothesis that children attending schools with the highest proportion of low-income students were more likely to miss school because of asthma than children attending schools with the lowest proportion of low-income students. We examined the relationship of school-level socioeconomic indicators with absenteeism while accounting for a wide range of individual-level factors including income, asthma severity, and health insurance status.

Seventeen percent of children aged 4 to 17 who attended public school had diagnosed asthma, of whom 23% had missed at least 1 day of school because of their asthma (Table 1). The first regression model indicated that children in the lowest family income group were more likely to miss school because of asthma than children in the highest income group, while adjusting for all other covariates (Table 2). In addition, younger children, those who had more frequent asthma symptoms, or those using prescription asthma medications were more likely to miss school because of asthma.

The results of the second model indicate that children attending schools with the highest proportion of low-income students were more likely to miss school because of asthma than children attending schools with the lowest proportion of low-income students (OR, 1.99; P = .03), while adjusting for age, sex, race/ethnicity, family income, insurance status, and severity of asthma (Table 2). Although the effect was somewhat attenuated, the association between family income and missing school because of asthma remained significant in model 2. As with model 1, younger children, children with more frequent asthma symptoms, or children taking prescription asthma medication also were more likely to miss school because of asthma.

This study found that students who attended schools with the highest concentrations of low-income students were more likely to miss school because of asthma than those at schools where the concentration of low-income students was lower. In addition to family income, the proportion of low-income students in the school is associated with asthma-related school absences after adjusting for family income, demographic characteristics, health insurance status, asthma severity indicators, and exposure to household smoke. Because California schools receive funding based on daily attendance, these findings suggest that resources allocated to schools with a large proportion of low-income students may be reduced because their children are more likely to miss school because of asthma (2,12,13). However, these findings also suggest that school-level interventions to help children manage their asthma may be explored as a strategy to decrease school absenteeism.

Our findings indicate that children from low-income families, who are younger in age, who have more frequent asthma symptoms, or who take daily prescription asthma medications were also more likely to miss school because of asthma. These findings are consistent with those of previous studies, which showed that children’s absences from school because of asthma were related to the underlying severity of their asthma (9). For instance, among children with asthma, those with more frequent asthma symptoms and those taking prescription asthma medications were more likely to miss school because of their asthma. Consistent with existing literature, our findings also showed that students from poor families were more likely to miss school than those from more affluent families (10,11).

Our analysis does not provide a direct explanation for why children attending schools with the highest concentrations of low-income students were more likely to miss school because of asthma. However, other research offers possible explanations. For example, students at disadvantaged schools may have higher exposure to indoor or outdoor asthma triggers. School absences are related to air pollution exposure (19,20). School location can determine exposure to air pollution, particularly traffic-related pollutants, and schools with a high proportion of students in the free and reduced-price meal program are more likely to be near busy roads (18). Furthermore, Simons et al found that students who attend schools with poor building conditions, such as visible mold, vermin, and poor ventilation, are more likely to miss school (21). In addition, they found that schools in lower SES districts show some of the strongest associations between poor building conditions and absenteeism. Poor building conditions may also lead to more intrusion of outdoor pollutants, such as motor vehicle exhaust (22).

School absences due to asthma can be avoided by appropriate asthma management, including appropriate use of medications and reduced exposure to triggers (23). Our results suggest that school-level interventions, especially in schools with high concentrations of low-income students, could be effective in decreasing school absenteeism due to asthma. Potential interventions could include indoor and outdoor air pollution control, for instance, locating schools, day care centers, and sports fields away from busy roadways. In 2003, California passed legislation (SB 352) that requires school districts to ensure that new schools are not built on old hazardous waste sites, hazardous release sites, or sites that contain pipelines that carry hazardous substances; in addition, school site boundaries cannot be within 500 feet from the edge of the closest traffic lane of a freeway or busy traffic corridor (24). This legislation could be a model for other states to follow.

School-based asthma education and disease management could be another effective measure to reduce absenteeism. For example, 1 study demonstrated that a comprehensive school-based asthma program led to fewer absences attributable to asthma (25). Other research suggests that children with asthma enrolled in schools without a school-based health center miss more days of school than those enrolled in schools with such a center (26). However, supplemental funding from public sources is likely needed for schools serving low-income populations to establish programs such as asthma education or school-based health centers, because these schools do not have the same capacity to raise funds from within the community as schools serving high-income populations. Many of these strategies are included in the Centers for Disease Control and Prevention’s Strategies for Addressing Asthma Within a Coordinated School Health Program (27).

This study has several limitations. First, the CHIS data, including our outcome indicator, school absence due to asthma, are self-reported. These data may be subject to recall bias or error in the self-reported asthma-related indicators. For instance, respondents might not be able to accurately recall the number of days of school missed due to asthma for more than the proximate past. As a result, we used the measure of 1 or more school days missed instead of actual number of school days missed, which may be less error prone. We also expect this error to be similar for those who attended schools with high or low concentrations of low-income students, that is, nondifferential with regard to SES of their schools. Second, our results are based on data from a single state, and the results may not be generalizable to all states. However, California is the most populous US state, with approximately 36.5 million residents, and its population is diverse. In addition, California often provides an early indication of health and policy trends for the rest of the nation. For example, California has more stringent state air quality standards than the nation and was the first state to regulate the siting of schools. As a result, the findings of this study could be informative for a national audience. Additionally, this study does not explain the underlying causes of school absences. Future research could examine these underlying causes by linking school-based environmental indicators, such as traffic near schools and air pollutant monitoring data, with asthma outcome data. Future research could also explore other indicators of neighborhood SES.

Although further studies are necessary to confirm the findings of this cross-sectional study and explore the underlying causes of school absences, these results suggest that school-level interventions, especially in schools with high concentrations of low-income students, should be explored as a strategy to decrease school absenteeism due to asthma. Potential interventions could include school-based asthma education and disease management and indoor and outdoor air pollution control.

This research was supported by a grant (no. 20081418) from The California Endowment. We thank Melanie Levy for her assistance with data analysis.