Grammar schools could look to boost their numbers in a bid to attract more funding, headteachers have suggested.
Heads are dealing with a squeeze on budgets, and expansion could be a "pragmatic decision" for some selective schools, according to the Association of School and College Leaders (ASCL).
Controversial proposals to lift the ban on creating new grammar schools were a key plank of the Conservative manifesto in last year's snap general election, but the plans were dropped in the wake of the election result, which saw the Tories lose their overall majority.
But grammars can still take on more pupils under rules that allow good state schools to expand.
Speaking as ASCL met for its annual conference in Birmingham, the union's deputy general secretary, Malcolm Trobe, said: "What we've seen talking with some of our grammar school head teachers is essentially the funding squeeze on them."
Grammar schools have significant numbers of 16 to 18-year-olds, Mr Trobe said, where there is a particular squeeze on funding.
"One of the ways they can help to address that squeeze is to increase their numbers. If they increase their numbers in their main school, because they're selective, it will automatically effectively increase their numbers post 16 in the long run.
"The other thing is that you can get economic numbers - economic unit size in a year group.
"So, what they are trying to do is move to a situation where they've got the most economically viable sized year groups going through the school. If you are a relatively small grammar school with 90 kids that's not a good economic unit to go forward.
"You're better on 120, 180 is better than 150, in the way that you can construct it. So, there are what I would call pragmatic decisions being made by grammar school heads.
"That's certainly the message I'm picking up."
Mr Trobe said ASCL did not know how many grammar schools may seek to expand.