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Mayor Bill de Blasio is canceling one of his signature education initiatives, acknowledging that despite spending $773 million he was unable to turn around many long-struggling public schools in three years after decades of previous interventions had also failed.

The end of the initiative, called Renewal, is a blow to Mr. de Blasio, who had hoped that success would bolster his effort to build a national reputation for innovative policies. Urban educators around the country had also looked to Renewal as a model for improving underperforming schools in historically troubled districts, rather than closing them.

Instead, the program has been plagued by bureaucratic confusion and uneven academic results since Mr. de Blasio began it in 2014. Though some of the nearly 100 low-performing public schools have shown better results, many have fallen short of the improvements that Mr. de Blasio predicted. The Renewal label itself caused parents to seek other options, causing enrollment in some schools to plummet.

The New York Times reported in October that Mr. de Blasio was preparing to close Renewal, and that city officials had known some Renewal schools were likely to fail but had left most of them open anyway. As a result, officials essentially kept thousands of children in classrooms where they had little if any chance of thriving.