An earlier post comparing the demographics of High Tech High and San Diego Unified School District included this table:

One interesting pattern was the apparent decline in poverty — measured by the number of students receiving free and reduced lunches — as students moved to higher grades. At San Diego’s public elementary schools, 63 percent of students qualify for free or reduced lunches; the number falls to 49 percent in high school.
Peter Bell, the district’s research director, said no one knows quite why this happens. But he said the district has three hypotheses:
- Students of lower socioeconomic status also tend to have higher dropout rates, so more of them may drop out before they get to high school;
- “The second possibility is that for families, their economic standing improves with the age of the parents. They tend the promotions and what not,” Bell said. In other words, parents tend to grow richer as their kids get older;
- “The third possibility is that there is some stigma attached to getting a free lunch. And we do know that high school students are less likely to apply than elementary students are,” he said. This last one, though, is becoming less of a problem, Bell explained, because parents may now fill out a single application for all of their kids, and families receiving public assistance no longer not need to apply at all.