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When schools are overcrowded, it doesn’t much matter to children (and their parents) whether developers are paying their share of the cost of adding capacity, because kids need space in classrooms (along with gymnasiums and cafeterias) in order to learn and thrive. That’s why the county’s growth rules, known as the Subdivision Staging Policy or SSP, prohibit new residential development in any school cluster where the schools are at 120 percent of capacity.

The “annual school test,” which determines whether a school cluster goes into a residential development moratorium, is applied in July of each year. The impact of a development moratorium is felt as new residential projects in an area are put on hold and, in some cases, subsequently fail to move forward at all because of market changes or the loss of financing.

The SSP is based on the common sense idea that growth should not get ahead of the public infrastructure needed to support it. One problem is that school enrollment growth does not track the overall rate of population growth as closely as you might think. This graph shows the relationship between Montgomery County Public Schools (MCPS) enrollment and the county’s population over the past few decades, with the school enrollment and total population indexed at 100 in 1990:

Enrollment shrank during the 1970s and 80s. The Baby Boom was over and MCPS was closing and repurposing schools as a larger proportion of the adult population aged out of their child-bearing (and raising) years. Beginning around 1990, a smaller but still significant demographic wave washed over the county and the rate of school enrollment growth began to outpace overall population growth. Many of the schools closed in the previous decades were now unavailable to absorb new students.

This long-term growth wave has continued. MCPS enrollment is expected to grow by about 11,000 students over the next six years:

Eventually, this wave will recede and the rate of growth in the school-age population will sink below the rate of growth in the all-ages population. Some demographic forecasts show this decrease happening within the coming decade. Other factors also influence the size of the MCPS population, such as the relative share of students in private versus public schools. In any event, the lesson here is that (at least for now) the number of schoolchildren is  growing faster than the overall rate of population growth and these kids will be in our schools whether or not more housing is built.

The relationship between the number of people who live in a specific neighborhood and the number of school-age children in that neighborhood varies even more widely than at the countywide level. In addition to the broad demographic trends that produce baby booms and busts at the national or regional level, neighborhoods go through their own cycles.

The consequence of this boom-and-bust cycle in individual neighborhoods is that areas popular with young families tend to see sharp spikes in school enrollment, even when there is little or no new residential development. This phenomenon is at work today in six county high school clusters at risk of entering a development moratorium in July. Take a look at this chart:

Enrollment Growth and New Development 

Six overcrowded clusters using enrollment and development data from 2011-2015

    New Multifamily Units New Single Family Attached Units
Cluster Enrollment Growth Units Built Students % of Growth SGR Units Built Students % of Growth SGR
Blair 1,095 1,412 51 4.7% 0.036
Einstein 652 1,014 32 4.9% 0.032
Northwood 693 862 19 2.7% 0.022 108 10 1.4% 0.093
Walter Johnson 761 1,094 27 3.5% 0.025 153 22 2.9% 0.144
Richard Montgomery 424 562 1 0.2% 0.002
Quince Orchard 532 328 22 4.1% 0.067
TOTAL 4,157 4,944 130 3.1% 0.026 589 54 1.3% 0.092


In the Quince Orchard High School cluster, no new multifamily buildings and only 328 new townhouses were built between 2011 and 2015. A total of 22 MCPS students lived in these new homes in 2015. Yet during the same time period, the Quince Orchard cluster’s enrollment grew by 532 students.

What about the Blair cluster, which has seen construction of new apartment buildings? During the same time period, enrollment in the Blair cluster grew by nearly 1,100 students while over 1,400 new units of multifamily residential were built. Surely, that many apartments must be a major cause of the overcrowding, right? Address and enrollment data show that only 51 MCPS students live in these apartments – less than five percent of the total growth in enrollment.

The story is the same for the other clusters on the brink of entering development moratoria. As you can see, enrollment in these six school clusters grew by 4,157 students, but only 184 MCPS students were living in the 5,533 new townhouse or multifamily dwelling units constructed during this period. Three years later, in 2018, these same units continue to generate students at a rate approximately 70% below similar units across the six clusters.  How is this possible? Why do some neighborhoods experience such rapid growth in the number of school age children that they can overwhelm existing schools even with little or no new residential development in the area? In the next post, I will provide some data and a theory, along with some additional complications in forecasting school enrollment.

3 Responses to “Schools and Growth, Part Three: New Development and Overcrowding”

  1. Tony Camilli

    Dear Casey,

    Great analysis and explanation, as always! I really enjoy your blog posts – they demystify the conspiracy theories and explain things in easy to understand terms and with real data to support the conclusions. Keep at it!

    This blog post in particular is one that has parents scratching their heads (or at least me), because I live in a MCPS cluster that continues to see large MCPS enrollment gains with little to no corresponding gains in housing units. And some parents conclude that any new housing development in my neighborhood is bad because “the schools are overcrowded.” As you show in this blog post, such an assumption is false and not supported by data. MoCo is lucky to have you running the Planning Department.

  2. Susan Fischet

    A better indicator of school population growth may be the number of apartment units and the occupancy rate of apartment dwellings in the school cluster. Purchasing a new home requires a certain degree of economic stability that is not required for apartment rental. But mire children including school age children can be housed in apartment units than single family/ townhomes

  3. Katya Marin

    How do you account for the difference between the SGR you calculate here (0.026), and the more recent rates for the County (0.139 countywide and 0.188 in the Blair/Einstein/Northwood region). Is the student generation rate going up since 2011-2015? Is that when the units were built, or when they were permitted? What was the vacancy rate in these new buildings at the point in time time that the students were counted? (And what about single family detached units?) Is it possible that the new units generate vacancies that families find more affordable, so that new development contributes to enrollment by trickling down to older housing instead of directly?