State lawmakers are likely to agree to a one-year extension of mayoral control of New York City schools, sources said Thursday evening.

Such an agreement would avoid the procedural mess that would result if lawmakers allowed mayoral control of the nation’s largest school district to expire. But it would also be a significant disappointment for the Mayor Bill de Blasio, who was unsuccessful at winning support in Albany for a longer-term deal last year.

According to a source close to the negotiations, Assembly Democrats, who have supported the mayor’s push for a three-year deal, have indicated that they will support a shorter agreement. The deal being discussed does not include a package of education tax credits that would benefit private schools, which de Blasio has said he does not support.

It could include some benefits for charter schools, though. One of the Senate’s mayoral control bills includes a provision that would allow charter school teachers to be eligible to teach for three years by completing a training program run by a charter school — a measure that would help large charter networks like Success Academy. The bill also gives charter schools more flexibility to switch authorizers.

Lawmakers are expected to come back Friday to finalize the deal and pass any remaining bills.