Schools and districts around the D.C. area rely on millions of dollars each year from private donors to finance building renovations, field trips and scholarships, but as wealthy areas receive small fortunes, others see much less.

In Maryland, the Montgomery County Public Schools Educational Foundation — the conduit for many of the private donations — had $2.9 million in assets, according to the most recent tax records, compared with about $550,000 in neighboring Prince George’s County’s fund.