A deterioration in critical thinking skills is being blamed for a continuing five-year decline in Grade 12 English diploma exam results.

Alberta Education suggested Tuesday that this might be due to an increased number of older teachers retiring who might be more adept at teaching these important skills.

But Jim Field, an professor of education at the University of Calgary, said the drop in critical thinking abilities in graduating teens is a byproduct of classroom conditions.

"I would hate to be an English 30 teacher with 45 kids in my classroom without room even to put their backpacks away," said Field. "You have to spend time teaching critical thinking. It develops over time. English 30 is a road race, you've got 13 weeks to teach seven novels and it's content driven. You've got to get your kids through the content because they test content on the exam.

"There isn't time to teach them to think critically, you have to get through all this stuff that's going to be on the exam."

Overall, the number of students who achieved the standard of excellence (80 per cent) on provincial achievement tests (for Grades 3, 6 and 9) rose by 1.1 per cent to 19.4 per cent in 2010 while those who met the acceptable standard (50 per cent) rose slightly by 0.8 per cent to 79.1 per cent.