When Kelly said that she had been placed in a virtual lab, Ms. Sutter recalled her “jaws dropped.” Neither of them had been told that Kelly would be in one.

“It’s totally different from what classroom teaching is like, so it’s a completely different animal,” Ms. Sutter said.

Under the state’s class-reduction amendment, high school classrooms cannot surpass a 25-student limit in core subjects, like English or math. Fourth- through eighth-grade classrooms can have no more than 22 students, and prekindergarten through third grade can have no more than 18.

Alix Braun, 15, a sophomore at Miami Beach High, takes Advanced Placement macroeconomics in an e-learning lab with 35 to 40 other students. There are 445 students enrolled in the online courses at her school, and while Alix chose to be placed in the lab, she said most of her lab mates did not.

“None of them want to be there,” Alix said, “and for virtual education you have to be really self-motivated. This was not something they chose to do, and it’s a really bad situation to be put in because it is not your choice.”

School administrators said that they had to find a way to meet class-size limits. Jodi Robins, the assistant principal of curriculum at Miami Beach High, said that even if students struggled in certain subjects, the virtual labs were necessary because “there’s no way to beat the class-size mandate without it.”

In response to parental confusion about virtual classes, the Miami Beach High parent-teacher association created a committee on virtual labs. The panel works with the school toward “getting issues on the table and working proactively,” said Patricia Kaine, the association’s president.