LONDON, ONT. -- Public high schools in London-Middlesex and Lambton and Kent counties were closed Wednesday as part of a one-day walkout by secondary school teachers at 10 boards across the province.

The Thames Valley District School Board (TVDSB) and Lambton-Kent District School Board (LKDSB) were among the affected boards.

The London District Catholic School Board (LDCSB) was not affected and their schools remain open.

Talks between the Ontario Secondary School Teachers' Federation (OSSTF) and the province reportedly ended earlier this week with a mediator saying the two sides were too far apart to continue.

No new talks are scheduled until the new year.

All elementary schools in the TVDSB and the LKDSB remained open, while bus transportation was cancelled only for the schools affected.

Teachers have not had a contract since the end of August.

Wage caps, class sizes and mandatory online courses are among the sticking points for the union, but Education Minister Stephen Lecce says the main issue is compensation.

Rural Schools have plenty to lose: Teachers' union

A small group of teachers and supporters marched in bitter cold in front of Ridgetown District High School, amid the province-wide one-day strike.

The educators say the key issues at the core of the impasse between the OSSTF and the province will hurt rural schools the most.

For example, increased class sizes, a pillar in the union fight, have deeply hurt small centres like Ridgetown, says Jennifer Kumpf, president of OSSTF District 10.

Kumpf says as class sizes increase, and programs that fail to meet the minimum are at risk. The situation leaves rural students with limited choices, forcing some to travel to schools further away just to maximize their education.

Kumpf says it’s a point lost on Premier Doug Ford, who pushed to improve rural and small-town life during the last election. Ford was sent to Queen’s Park with strong support from less densely populated areas of Southwestern Ontario.

Ridgetown is the smallest high school in the Lambton-Kent District School Board.

A teacher at the school tells CTV News there are just 12 full-time equivalent educators teaching high school courses.

The building also houses grade seven and eight students. Those students were in class Wednesday.

- With files from and The Canadian Press