This study examined the regular infringement of outside intrusions into the classroom learning environment, surveying a stratified, randomly-selected group of 557 teachers in Saskatchewan, Canada, regarding their experiences with and feelings about such time-consuming episodes. Teacher were asked to indicate the typical daily number of such occurrences, the types of interruptions, and their feelings about them. Results indicated that almost all of the teachers experienced interferences from outside the physical parameters of the classroom. Almost half reported experiencing such interruptions only twice a day, while more than one-third reported such intrusions three to four times a day, and the rest reported such interruptions at least five or six times per day. The main source of classroom interference, by far, was the public address system, followed by message delivery, unspecified visitors, other teachers, other students, parents, and the telephone. While there was a wide variation in the reported impact of these interruptions on teachers' classes, more than half of the teachers indicated that they were a serious problem. (Contains 31 references.) (SM)