SAN FRANCISCO (CBS SF) – San Francisco teachers and teaching aides apparently missed much more class than the average student last year.

The San Francisco Chronicle has reported that the average instructor was absent 11 school days during the 2013-2014 year, while the typical student missed fewer than seven days. That means teachers were absent, on average, 6.6 percent of the time while students missed 3.7 percent of their scheduled school time.

A that rate, teachers miss a day about once every three weeks during the school year, which is comparable to other similar districts but higher than many other industries, according to the paper.

Some explain that teachers are confined in rooms with dozens of people and are potentially exposed to more germs than people in other fields, but others note that the absences are often clustered around scheduled breaks.

The issue came to a head last year when several hundred teachers called out sick the day before the Thanksgiving break, forcing San Francisco Unified to scramble to find substitutes.

The current school year got going Monday, and San Francisco teachers have threatened to strike if they don’t get a 22 percent pay raise over the next three years in an attempt to keep pace with the skyrocketing cost of living in San Francisco.