Eva Moskowitz has had an epiphany: A longer school day is not necessarily a bonus for teaching and learning.

In a remarkable about-face, the founder and CEO of Success Academy announced in December that the chain of charter schools will shorten its school day. Beginning next fall, the elementary school day will be 45 minutes shorter, and middle schools will have 90 minutes lopped off their day.

“We have found that the length of our current school day is difficult for both scholars and teachers,” Moskowitz stated in an internal staff memo obtained by Politico New York. “It doesn’t leave enough time for clubs, sports programs, and the tutoring and extra support that some scholars need. It is also challenging for staff to find enough personal time to recharge and be at their professional best.”

Many charter schools believe the longer day is a magic bullet. It’s not. Most experienced educators can tell you that the best schools are joyful places for both teachers and students. But long hours of test prep do little to ignite a love of learning in students and are exhausting, particularly for younger children.

The long school day has also likely contributed to high teacher turnover. According to the most recent state data obtained by The New York Times, nine Success schools had teacher attrition rates of more than 40 percent, and three had attrition rates of more than 50 percent in the 2013–14 school year.

Some will say that the shorter day will make Success Academies more like public schools. But that comparison won’t be apt until the charter chain does a better job of recruiting and retaining its most challenging students. In October, Moskowitz disavowed the “Got to Go” list of weak and challenging students that one Success principal had created. But list or no list, as long as the charter chain embraces only higher-performing students, it won’t be fulfilling the historic mission of New York City public schools: to serve all children.