Cellphones will be banned in Ontario classrooms during instructional time, starting in September.

Education Minister Lisa Thompson said in a statement Tuesday that a formal announcement is coming soon.

"Ontario's students need to be able to focus on their learning — not their cellphones," she wrote. "By banning cellphone use that distracts from learning, we are helping students to focus on acquiring the foundational skills they need, like reading, writing and math."

Some schools already have similar policies, but the province will issue a directive to all public schools for the 2019-20 school year, government sources told The Canadian Press. How to enforce the ban would be up to individual boards and schools.

Exceptions would be made for when teachers want to use cellphones as part of their lesson, for medical reasons and students with special needs.

The Tory government conducted education consultations last year and, while input on the sex-education curriculum dominated headlines, feedback was also gathered on a potential classroom cellphone ban.

About 97 per cent of respondents favoured some sort of restriction on phones in class.

"It was the closest thing we got in our consultation to unanimity," one source said.

The Progressive Conservatives had proposed such a ban in their platform during last year's election campaign.

Enforcement could be a challenge, school board finds

The Toronto District School Board used to have a cellphone ban, but reversed it after four years to let teachers dictate what works best for their classrooms. The board has previously said that enforcing an outright ban was next to impossible, and said that to curb technology use would be to place limits on educational opportunities as well.

A 2015 London School of Economics and Political Science paper found that "student performance in high stakes exams significantly increases" with a ban on mobile phones. The improvements were largely seen among the students who were normally the lowest achieving.

"This suggests that restricting mobile phone use can be a low-cost policy to reduce educational inequalities," the study found.