The policy on what are known as "split" classes applies to students in grades one to four. It means, for example, that if there were 36 first graders at a school, the principal would have to place six of them in a class with second graders rather than creating two classes of first graders or allowing one large class. The class-size limit in kindergarten and grades one to three is 30 students; it is 33 students in upper grades.

Education advocates and the Philadelphia Federation of Teachers oppose the policy directive, which they say puts children's education at risk by requiring a teacher to teach two different curriculums in classes that are too large and have children with high needs.

Officials could not say how many schools would be penciled in for the split classes.

"Split classes are not best for children, especially very young children in grades one, two and three," said PFT president Jerry Jordan. "This is not the way to go."

District officials say this is just a routine procedure early on in the budgeting process and that ultimately split classes will not exist.

"It is our intention not to have any oversize or split-grade classes" when school starts in September, said Cassandra W. Jones, interim chief academic officer.

Parents and union officials are skeptical.

"We were promised that they don't want any split classes, but here it is," Greg Wade, president of the Home and School Council said, referring to the budget memo.

Added Jordan: "Principals are being told, this is what you do."

The memo reads: "In elementary schools, if splits are required to maintain contracted class size . . . then they must be formed. Teachers and principals cannot agree to oversize classes to avoid split grades."

The policy does not apply to kindergarten or grades five to eight.

Jones said principals are being directed to create split classes so that the central office can see where problems exist. Then the staff will work with principals to figure out a way to redeploy personnel to avoid the split or add staff if necessary, she said.

"It's a work in progress," she said.

If a split class appears unavoidable, both the principals' union and teachers' union will be notified, Jones said.

Parent Helen Gym of Parents United for Public Education said that multi-age classrooms can work if the teacher chooses them for educational reasons, prepares for them, and has the proper curriculum. But she opposes them when they are a "forced situation," as they have been in the Philadelphia district.

"It's not based on academics, it's based on budgets," she said. "The teacher may or may not be prepared."

Last spring, the School Reform Commission agreed to add 130 teaching positions back into the budget and in August directed that they be used to reduce class sizes in the lower grades and eliminate split classes. As a result, there are only three split classes in the district this school year, compared with 45 in 2006-07, Jones said.

Former chief executive officer Paul Vallas reduced split classes over his tenure that began in 2002, but last year his administration increased the number after a budget deficit emerged, yielding complaints from parents and union officials.