TORONTO -- Some Ontario school boards have written to the education minister with concerns that planned increases to class sizes will mean they can offer fewer elective courses, such as in the arts and skilled trades.

Lisa Thompson announced last month that average high school class sizes will increase by six students -- from 22 to 28 -- a change to be phased in over four years.

School boards in Peel region, Toronto and eastern Ontario wrote to the minister with concerns about the move.

They say increased class sizes will mean fewer teachers will be needed in schools and that will put some programs that schools currently offer in jeopardy.

Thompson says larger class sizes won't make a difference to students, rather the quality of the teacher is what matters.

Students are planning a walkout Thursday to protest Thompson's education changes, including class sizes.