Leonie Haimson is executive director of Class Size Matters. She has worked tirelessly to persuade legislators in New York State to limit class sizes. Her efforts were successful in the latest legislative session when both houses passed limits on class sizes.

However billionaire Michael Bloomberg, who was mayor of New York City for 12 years, has been an outspoken critic of class size reduction. In this article that appeared on Valerie Strauss’s “Answer Sheet,” Haimson explains why Bloomberg is wrong.

Strauss writes:

In 2014, I wrote this: “Every now and then someone in education policy (Arne Duncan) or education philanthropy (Bill Gates) …. will say something about why class size isn’t really very important because a great teacher can handle a boatload of kids.”


Well, some can do that, but anybody who has been in a classroom knows the virtues of classes that are smaller rather than larger even without the research that has been shown to bear that out.


Now the issue is back in the spotlight, this time in New York City, where a new state law requires the public school system — the largest in the country — to reduce class sizes over five years. Opponents of the law are pushing back, especially Mike Bloomberg, mayor of New York City from 2002 to 2013. He called for smaller class sizes in his first mayoral campaign but has now changed his mind.


In an op-ed in several publications, Bloomberg says students don’t need smaller classes but better schools — as if the two were entirely unrelated — and he ignores research, such as a 2014 review of major research that found class size matters a lot, especially for low-income and minority students.

This post, written by Leonie Haimson, looks at the issue, and Bloomberg’s position. Haimson is executive director of Class Size Matters, a nonprofit organization that advocates for smaller classes in New York City and across the nation as a key driver of education equity.

By Leonie Haimson


The knives are out against the new class size law, overwhelmingly passed in the New York State Legislature in June 2022, requiring New York City schools to phase in smaller classes over five years, starting this school year. The law calls for class sizes in grades K-3 to be limited to no more than twenty students; 23 students in grades 4-8, and 25 in core high school classes, to be achieved by the end of the 2027 school year. The law was passed despite the opposition of the city’s Department of Education officials, who insist that it will be too expensive, and somehow inequitable, because, they say, the highest-need students already have small enough classes.

Most recently, Mike Bloomberg, the former mayor of New York City and an adviser to Mayor Eric Adams, published identical opinion pieces in three major outlets: Bloomberg News (which he owns), The Washington Post, and the New York Post, inveighing against the goal of lowering class sizes. His piece is clearly meant to sway opinion leaders and legislators to repeal the law, and because of his prominent position, some may listen without knowing about fundamental problems in his op-ed.

Class size reduction has been shown as an effective way to improve learning and engagement for all students, especially those who are disadvantaged, and thus is a key driver of education equity. The Institute of Education Sciences cites lowering class size as one of only four education interventions proven to work through rigorous evidence; and multiple studies show that it narrows the achievement or opportunity gap between income and racial groups.

Bloomberg claims that because of the initiative, “City officials say they’ll have to hire 17,700 new teachers by 2028.” Actually, the estimate from the New York City Department of Education (DOE) itself is far smaller. In their draft class size reduction plan, posted on July 21, DOE officials estimated that 9,000 more teachers would be required over five years. While it’s true that the Independent Budget Office estimated the figure cited by Bloomberg, this large disparity between the two figures appears to stem from the fact that, as the IBO pointed out, the DOE’s budget already includes 7,500 unfilled teaching positions, which schools have not been allowed to fill. While Bloomberg claims the cost will be $1.9 billion for staffing, the DOE’s own plan estimates $1.3 billion — and these costs could be considerably lower if they redeployed teachers who are currently assigned to out-of-classroom positions to the classroom to lower class size.

The legislature passed the new law in recognition that the city’s DOE is now receiving $1.6 billion in additional state aid to finally settle the Campaign for Fiscal Equity lawsuit launched more than 20 years ago. In that case, the state’s highest court found that, because of excessive class sizes, the city’s children were deprived of their constitutional right to a sound, basic education.

Yet since his election, Adams has repeatedly cut education spending, and now threatens to cut it even more, by another 15 percent. As a result of these cuts, class sizes increased last year and will likely be larger this year. Hiring enough teachers to meet the law’s requirements will be a challenge in any case, but it will be impossible to achieve if the administration’s repeated cuts and hiring freezes are implemented.

Yet in the end, smaller classes would likely strengthen teacher quality by lowering teacher attrition rates, especially at our highest-need schools, as studies have shown.

In his op-ed, Bloomberg claims that creating the additional space necessary to lower class size will cost $35 billion, which is misleading. DOE did include this estimate in its original May 2023 draft class size plan. However following pushback by critics who pointed out that this figure bore no relation to reality, they deleted that inflated estimate in their more recent July class size plan. If DOE equalized or redistributed enrollment across schools, this would likely save billions of dollars in capital expenses. Right now, there are hundreds of underutilized public schools, sitting close by overcrowded schools that lack the space to lower class size.

Bloomberg, echoing an erroneous DOE claim that funds spent on lowering class size will not help the highest-need students, wrote: “Under the new mandate, only 38 percent of the highest-poverty schools would see class sizes shrink, compared to nearly 70 percent of medium- to low-poverty schools … it won’t help the students who need it most.”

Actually, only 8 percent of schools with the highest poverty levels (with 90 percent or more low-income students) fully complied with the class size caps last year, according to an analysis by Class Size Matters. Thus, 92 percent of these schools would see their class sizes shrink if DOE complied with the law, rather than the 38 percent that Bloomberg claims.

Moreover, by solely focusing on schools with 90 percent poverty levels or more, his claims are misleading. A piece in the education publication Chalkbeat attempted to make a similar argument, by using class size data provided by DOE that shows that 68 percent of classes in the highest-poverty schools met the class size limit. This is far different than Bloomberg’s claim that 68 percent of these schools are achieving the limits in all of their classes.

In addition, the class size data, analyzed in conjunction with DOE demographic data, shows that there are many more NYC public schools in the other two categories summarized by Chalkbeat, “Low-to-Mid Poverty” (schools with 0-75 percent low-income students) and “High Poverty” (schools with 75 percent to 90 percent low-income students), than those in their “Highest Poverty” category. Most importantly, these two categories of schools enroll a supermajority of our highest-needs students.

In fact, 79 percent of low-income students, 78 percent of Black students, 74 percent of Hispanic students, and 74 percent of English-language learners are enrolled in these other two categories of schools, while only 21 percent to 26 percent of these students are enrolled in the “Highest Poverty” category.

This further indicates that without a citywide mandate to lower class size, smaller classes would likely never reach most of our most disadvantaged students.

Indeed, the highest-needs students, including students of color, low-income students, and English-language learners, have been shown to gain twice the benefits from smaller classes in terms of higher achievement rates, more engagement, and eventual success in school and beyond, which is why class size reduction is one of very few education reforms proven to narrow the achievement or opportunity gap. Thus, by its very nature, lowering class size is a key driver of education equity.

There is also no guarantee that the smaller classes in our highest poverty schools will be sustained without a legal mandate to do so. In July, DOE officials omitted the promise in their May class size plan that schools that had already achieved the caps would continue to do so, as pointed out by a letter signed by over 230 advocates, parents, and teachers. In fact, we found that fewer of the schools in every category achieved the class size caps last year compared to the year before.

Only 69 schools citywide fully met the caps in the fall of 2022, compared to 89 in the fall of 2021, and the number of students enrolled in those schools declined from 18,248 to only 13,905, a decrease of nearly 25 percent. Fewer still will likely do so this year.

So given that the data does not back up his claims, why is Bloomberg so apparently enraged at the notion that public school students would be provided the opportunity to benefit from smaller classes.

One should recall that when he first ran for mayor more than 20 years ago, Bloomberg himself promised to lower class size, especially in the early grades. His 2002 campaign kit put it this way: “Studies confirm one of the greatest detriments to learning is an overcrowded classroom … For students a loud packed classroom means greater chance of falling behind. For teachers, class overcrowding means a tougher time teaching & giving students attention they need.”

Yet class sizes increased sharply during the Bloomberg years, and by 2013, his last year in office, class sizes in the early grades in public schools had risen to the highest levels in 15 years. By that time, he had long renounced his earlier pledge, and had proclaimed in a 2011 speech that he would fire half the teachers and double class sizes if he could, and this would be a “good deal for the students.”

Bloomberg’s main educational legacy in New York City was a huge increase in the number of charter schools as a result of his decision to provide them free space in public school buildings, and his successful effort to persuade state legislators to raise the charter cap. During his three terms in office, the number of charter schools in the city exploded from 19 to 183.

Since leaving office, Bloomberg has continued to express his preference for charter schools, and has pledged $750 million for their further expansion in the city and beyond. A close reading of his op-ed suggests that one of the main reasons for his vehement opposition to the new law is because lowering class size may take classroom space in our public schools that, in his view, should be used instead for charter schools.

Indeed, he concludes the op-ed by saying “it would help if Democratic leaders were more supportive of high-quality public charter schools,” and goes on to rail against a recent lawsuit to block the Adams administration’s decision to co-locate two Success charter schools in public school buildings in Brooklyn and Queens — a lawsuit filed on the basis that it would diminish the space available to lower class size for existing public school students.

Of the $750 million Bloomberg pledged for charter expansion, $100 million was specifically earmarked for Success Academy. Regarding the lawsuit, launched by the teachers union along with parents and educators in the affected schools, Bloomberg writes, “It was an outrageous attack on children, and thankfully, it failed.”

Misleading people about the value of small classes to teachers and students as well as about class size data seems to be an attack on opportunities for New York City public school children, who deserve better. Class Size Matters hopes these efforts fail.