City officials say that boosting kindergarten readiness is important because it can start students on a successful school career.

"We understood that many of our kids were coming to school already at risk, and the need to remediate put the entire school system in a catch-up mode that we were never leaving," city schools CEO Andrés Alonso said.

While the city's percentage of fully ready students still trails some other school districts, the city had the biggest gain in Maryland.

Baltimore County's 87 percent remained flat, as did Anne Arundel County's 86 percent. Howard County increased from 87 percent to 89 percent. Carroll County saw a slight increase from 95 percent to 96 percent.

The percentage of students deemed ready in Prince George's County, which has a population similar to Baltimore's, fell from 77 percent to 73 percent in 2012. And even high-performing Montgomery County saw a slight decline, from 81 percent to 80 percent.

Other Baltimore-area school districts said that they, too, are in the process of aligning their pre-K curricula with the common core standards, with most expecting full rollouts next school year.

For instance, Baltimore County is going through pre-K curriculum revisions and professional development, and is developing what it calls a "world class Reading/English/Language Arts curriculum" for kindergarten through sixth grade.

Anne Arundel and Howard fully implemented the state's pre-K common core math standards this school year, and their language arts curricula will follow in the fall. Carroll County also has made substantial revisions in math.

A statewide emphasis on early-childhood education has boosted the percentage of Maryland students who enter kindergarten "fully ready" — from 49 percent in 2002 to 82 percent in 2012.

Officials said the state still needs to work on providing access, but Maryland has become a national leader in early-childhood efforts. It was one of nine states that won a $50 million federal Race to the Top grant for early-childhood initiatives in 2011.

The grant has spurred a number of initiatives, including the creation of local early-childhood councils, a rating system for parents to evaluate programs, and revising the state's readiness assessments.

Grafwallner said the state plans to dig deeply into the data to examine why Maryland's scores flatlined this year.

In the case of Prince George's County's significant drop, he said that systemic changes such as the county cutting its pre-K program to half-a-day had an impact.

Baltimore is the only large school district in the state that offers a full-day program to participating students, district officials said. Garrett and Kent counties do as well, but serve only 86 and 119 students, respectively.

Grafwallner said that for the other Maryland districts — all of which have seen 20 to 50 percentage-point gains in the last decade — it is not unusual for scores to plateau when they surpass 80 percent.

"It has called for readjustment, because the level of preparedness is much higher," he said, "and that's where the common core comes in."

Expansion

Alonso said the district recognized the value of early interventions years ago.

In 2009, the schools chief directed $32 million toward offering more pre-K seats and expanding the program to full-day.

"This was about looking ahead," Alonso said. "We knew that it was a once-in-a-lifetime funding opportunity, and we wanted to invest it in a way that would yield results in the long term."