CMS's extra teachers: Do the math

"Weighted student staffing" is a crucial part of Charlotte-Mecklenburg Schools' strategy for helping disadvantaged kids. It's going to play prominently in tough budget talks that lie ahead.

That's a challenge. Weighted student staffing involves -- pause for a collective shudder -- math formulas. That makes it tough to understand, and even tougher to explain in the limited space of a newspaper article designed for people reading quickly.

I've been fudging through the early budget articles with a vague description of extra teachers based on school poverty. My colleague Eric Frazier did an excellent job Sunday describing how high schools that don't get much help from weighted student staffing are seeing some class sizes balloon.

Unfortunately, while the data on class sizes was correct, we fumbled the description of the weighted student staffing formula.

It's important for people to understand this calculation going into 2011 budget. I figure blog readers are a good place to start; you're likely to stick with it and even suggest ways to make it clear to less dedicated readers.

Weighted student staffing starts with the premise that schools get teacher positions based on enrollment. Assuming a ratio of one teacher per 25 students (actual ratios vary from 1:22 to 1:29.5, depending on grade level), a school with 1,000 students would get 40 teachers paid by the state.

CMS uses county money to provide more teachers for disadvantaged kids. Lunch subsidies to low-income families are used as a rough measure of disadvantage (yes, I know there are questions about those numbers; that's a whole different topic). Each child who qualifies for lunch aid is counted as 1.3 students in the CMS formula.

So consider two schools with 1,000 students each. School A has a 20 percent poverty level, or 200 low-income kids. (Twenty percent is low by CMS standards; that's where South Charlotte Middle landed last year.) School B has 80 percent, or 800 kids.

School A is tallied as having 60 extra kids, based on multiplyng those 200 by 1.3. That would net about two more teachers.

School B gets credit for 240 extra kids, or almost 10 more teachers.

Why care? Because CMS is pumping $48 million a year into putting just over 800 additional teachers into schools based on that formula. They're not exclusively in high-poverty schools, as the example above shows, but most of them are.

Starting at the Dec. 14 meeting, the school board will start studying ways to cut roughly $100 million from the 2011-12 budget, which they'll vote on in May. That $48 million is sure to get scrutiny.

As controversial as it was to close buildings, many would say it's far more important to keep good teachers with kids. Brutal choices are looming. That means those of us who care about kids and taxes will need to pay close attention -- even if that means dealing with math formulas.